Abiotic stresses trigger premature leaf senescence by affecting some endogenous factors, which is an important limitation for plant growth and grain yield. Among these endogenous factors that ...regulate leaf senescence, abscisic acid (ABA) works as a link between the oxidase damage of cellular structure and signal molecules responding to abiotic stress during leaf senescence. Considering the importance of ABA, we collect the latest findings related to ABA biosynthesis, ABA signaling, and its inhibitory effect on chloroplast structure destruction, chlorophyll (Chl) degradation, and photosynthesis reduction. Post-translational changes in leaf senescence end with the exhaustion of nutrients, yellowing of leaves, and death of senescent tissues. In this article, we review the literature on the ABA-inducing leaf senescence mechanism in rice and
starting from ABA synthesis, transport, signaling receptors, and catabolism. We also predict the future outcomes of investigations related to other plants. Before changes in translation occur, ABA signaling that mediates the expression of
,
, and
transcription factors (TFs) has been investigated to explain the inducing effect on senescence-associated genes. Various factors related to calcium signaling, reactive oxygen species (ROS) production, and protein degradation are elaborated, and research gaps and potential prospects are presented. Examples of gene mutation conferring the delay or induction of leaf senescence are also described, and they may be helpful in understanding the inhibitory effect of abiotic stresses and effective measures to tolerate, minimize, or resist their inducing effect on leaf senescence.
Development of rice cultivars with low phytic acid (lpa) is considered as a primary strategy for biofortification of zinc (Zn) and iron (Fe). Here, two rice genotypes (XS110 and its lpa mutant) were ...used to investigate the effect of P supplies on accumulations and distributions of PA, Zn, and Fe in rice grains by using hydroponics and detached panicle culture system. Results showed that higher P level increased grain PA concentration on dry matter basis (g/kg), but it markedly decreased PA accumulation on per grain basis (mg/grain). Meanwhile, more P supply reduced the amounts and bioavailabilities of Zn and Fe both in milled grains and in brown grains. Comparatively, lpa mutant was more susceptive to exogenous P supply than its wild type. Hence, the appropriate P fertilizer application should be highlighted in order to increase grain microelement (Zn and Fe) contents and improve nutritional quality in rice grains.
MicroRNAs regulate and control the growth and development of cells and can play the role of oncogenes and tumor suppressor genes, which are involved in the occurrence and development of cancers. In ...this study, DNA fragments obtained by target-induced rolling-circle amplification were constructed to complement with self-cleaving deoxyribozyme (DNAzyme) and release fluorescence biomolecules. This sensing approach can affect multiple signal amplification permitting fluorescence detection of microRNAs at the pmol L
level hence affording a simple, highly sensitive, and selective low cost detection platform.
High temperature (HT) is the major environmental factor affecting grain starch properties of cooking rice cultivars. However, little information has been available on the effect of environmental ...temperature on the starch granule size distribution of rice grains. In this paper, five indica rice genotypes, including the wild type (9311) and its four mutants differing in amylose content (AC), were used to investigate the effect of environmental temperature on the starch granule size distribution, as well as its relation to AC and gelatinization properties of rice starch. Two temperature treatments (HT and NT) at filling stage were imposed to rice plants under the controlled temperature chambers. The result showed that HT increased the average diameter of starch granules and enhanced the proportion of large starch granules (LSG, D > 2.6 μm) by number, volume and surface area, respectively. However, influence of HT on GT and starch granule size distribution was relatively independent of their alteration in AC level for different rice genotypes. Therefore, HT-induced increase in the average diameter of starch granules and LSG percentage was strongly responsible for the higher starch gelatinization temperature and inferior cooked palatability of HT-ripening rice grains, which be not inherently associated with their varying AC level.
•HT exposure increased the average diameter of starch granules and altered the granule size distribution of rice starch.•HT-induced increase in LSG percentage was strongly responsible for the elevated GT value of rice starch under HT growth.•Effect of HT exposure on granule size distribution was relatively independent of the genotypic difference in AC level.
To clarify the relationship of sugar starvation with ABA-induced ROS generation during leaf senescence, the genotype-dependent differences in sugar concentration, endogenous ABA content, and ROS ...generation as well as their temporal patterns during leaf senescence were investigated by using two rice genotypes, namely, Zhehui7954 and its corresponding mutant with the premature senescence of flag leaves (
psf
). Meanwhile, the interplay between sugar starvation and ABA metabolism in the induction of leaf senescence was examined using detached leaves. The results showed that the
psf
mutant differed evidently from its wild type (Zhehui7954) in the temporal pattern of soluble sugar, sucrose and hexose (fructose and glucose) contents during leaf senescence, with the rapidly dropping concentrations of total soluble sugar, and sucrose, and hexose for the senescing leaves of
psf
mutant. Sugar starvation evidently accelerated leaf senescence and significantly enhanced the ABA concentration and malonaldehyde (MDA) accumulation in detached leaves, while exogenous sugar supply severely suppressed the ABA concentration and ROS level in detached leaves, thereby the delayed leaf senescence for the detached leaves treated by exogenous sugar supply. Correspondingly, ABA biosynthesis inhibitor (NDGA) effectively retarded the sugar starvation-induced leaf senescence, while ABA catabolism inhibitor (DNCZ) obviously accelerated leaf senescence by enhancing the endogenous ABA concentration in senescent leaves. Furthermore, sugar starvation severely repressed the transcripts of several key genes related to ABA biosynthesis and its degradation (
NCED1
,
NCED4, NCED5, ABA8ox2
and
ABA8ox3
), with the significantly lower amount of their transcriptional expression in the senescent leaves of
psf
mutant relative to its wild type during leaf senescence. Hence, the disequilibrium between ABA biosynthesis and catabolism was strongly responsible for sugar starvation-induced leaf senescence, which was derived from the suppression of ABA degradation, rather than the enhancement of ABA biosynthesis.
D1 protein in the PSII reaction center is the major target of photodamage, and it exhibits the highest turnover rate among all the thylakoid proteins. In this paper, rice psf (premature senescence of ...flag leaves) mutant and its wild type were used to investigate the genotype-dependent alteration in PSII photo-damage and D1 protein turnover during leaf senescence and its relation to ABA accumulation in senescent leaves. The symptom and extent of leaf senescence of the psf mutant appeared to be sunlight-dependent under natural field condition. The psf also displayed significantly higher levels of ABA accumulation in senescent leaves than the wild type. However, the premature senescence lesion of psf leaves could be alleviated by shaded treatment, concomitantly with the strikingly suppressed ABA level in the shaded areas of flag leaves. The change in ABA concentration contributed to the regulation of shade-delayed leaf senescence. The participation of ABA in the timing of senescence initiation and in the subsequent rate of leaf senescence was closely associated with PSII photodamage and D1 protein turnover during leaf senescence, in which the transcriptional expression of several key genes (psbA, psbB, psbC and OsFtsH2) involved in D1 protein biosynthesis and PSII repair cycle was seriously suppressed by the significantly increased ABA level. This response resulted in the low rate of D1 protein synthesis and impaired repair recovery in the presence of ABA. The psf showed evidently decreased D1 protein amount in the senescent leaves. Both the inhibition of de novo synthesized D1 protein and the slow rate of proteolytic removal for the photodamaged D1 protein was among the most crucial steps for the linkage between light-dependent leaf senescence and the varying ABA concentration in psf mutant leaves. OsFtsH2 transcriptional expression possibly played an important role in the regulation of D1 protein turnover and PSII repair cycle in relation to ABA mediated leaf senescence.
Ambient temperature and nitrogen (N) fertilizer are two of the most important factors that affect rice grain quality. However, less information has been available on the interactive effect of N ...fertilizer and ambient temperature on grain quality under stressful high temperature (HT). In this article, the effects of panicle N fertilizer, ambient temperature, and their interaction on starch composition, particle size distribution of starch granules, starch physicochemical properties, and storage protein accumulation in milled grains were investigated to clarify the potential role of panicle N fertilizer topdressing in regulating rice grain quality under stressful HT by using a two-factor experiment of three N levels in combination with two temperature regimes. Results showed that appropriate application of panicle N fertilizer could attenuate the adverse effect of HT during grain filling on milling quality and chalky occurrence to some extent, particularly for the effective alleviation of HT-induced decrease in milling quality. However, the topdressing of panicle N fertilizer tended to enhance starch gelatinization enthalpy (ΔH) and its setback viscosity in HT-ripening grains, with the simultaneous decrements in the number and surface area proportions of smaller starch granules under the higher N fertilizer in combination with HT exposure. The effects of higher nitrogen fertilizer and HT exposure on total protein content and gluten composition of grains were additively increased. Hence, the topdressing of panicle N fertilizer exacerbated HT-induced deterioration in cooking and eating quality, rather than alleviating the negative impact of HT exposure on the palatability of cooked rice.
The breeding of low phytic acid (
lpa
) crop is considered as an effective strategy to improve crop nutrition, but these crops have an inferior performance in seed germination. In this paper, two ...rice genotypes,
cv
. 9311 and its
lpa
mutant (9311-
lpa
), were used to clarify the relationship of InsP
3
and ROS concentration in sprouting seeds with the occurrence of retarded seed germination for
lpa
crop. Results showed that the inferior performance of seed germination for 9311-
lpa
was mostly characterized by the delay of seed germination progression, with insignificant difference in seed germination rate between the two genotypes after a longer imbibition duration. The retarded seed germination of 9311-
lpa
was closely associated with the genotypic difference in InsP
3
and ROS concentrations in germinating seeds, with the considerably higher InsP
3
level and lower ROS concentration for 9311-
lpa
relative to the wild type. Under an appropriate range of concentration, exogenous H
2
O
2
treatment promoted seed germination, while the activator of InsP
3
(
m
-3M3FBS) had an inhibitory effect on seed germination. The delay of seed germination occurred mainly as the results of the higher InsP
3
level and the lower ROS concentration in the germinating seeds of 9311-
lpa
. Furthermore, the germinating seeds of 9311-
lpa
had relatively lower activities of ROS scavenging enzymes (SOD, CAT, POD, and APX) and ROS generating enzyme (NOX) than those of the wild type.
m
-3M3FBS significantly suppressed NOX activity and NOX transcripts in sprouting seeds, which then resulted in the lowered ROS generation in sprouting seeds and the decreased seed germination rate. Thus, the retarded seed germination of 9311-
lpa
, with lower ROS level in germinating seeds, was mostly caused by the weaker ability of ROS generation in the presence of higher InsP
3
level, rather than the effective detoxification of ROS burst during seed germination.
Key message
HT-induced ROS burst in developing anther is closely related to the lowered CAT activity as the result of the markedly suppressed
OsCATB
transcript, thereby causing severe fertility ...injury for rice plants exposed to HT at meiosis stage.
The reproductive stage of rice plants is highly sensitive to heat stress. In this paper, different rice cultivars were used to investigate the relationship of HT-induced floret sterility with reactive oxygen species (ROS) detoxification in rice anthers under well-controlled climatic conditions. Results showed that high temperature (HT) exposure significantly enhanced the ROS level and malondialdehyde (MDA) content in developing anther, and the increase in ROS amount in rice anther under HT exposure was closely associated with HT-induced decline in the activities of several antioxidant enzymes. For various antioxidant enzymes, SOD and CAT were more susceptible to the ROS burst in rice anther induced by HT exposure than APX and POD, in which SOD and CAT activity in developing anther decreased significantly by HT exposure, whereas APX activity was relatively stable among different temperature regimes. HT-induced decrease in CAT activity was attributable to the suppressed transcript of
OsCATB
. This occurrence was strongly responsible for HT-induced increase in ROS level and oxidative-damage in rice anther, thereby it finally caused significant reduction in pollen viability and floret fertility for the rice plants exposed to HT during meiosis. Exogenous application of 1000 µM salicylic acid (SA) may alleviate HT-induced reduction in pollen viability and floret fertility, concomitantly with the increased CAT activity and reduced ROS level in rice anther.
Nitrogen (N) is a basic building block that plays an essential role in the maintenance of normal plant growth and its metabolic functions through complex regulatory networks. Such the N metabolic ...network comprises a series of transcription factors (TFs), with the coordinated actions of phytohormone and sugar signaling to sustain cell homeostasis. The fluctuating N concentration in plant tissues alters the sensitivity of several signaling pathways to stressful environments and regulates the senescent-associated changes in cellular structure and metabolic process. Here, we review recent advances in the interaction between N assimilation and carbon metabolism in response to N deficiency and its regulation to the nutrient remobilization from source to sink during leaf senescence. The regulatory networks of N and sugar signaling for N deficiency-induced leaf senescence is further discussed to explain the effects of N deficiency on chloroplast disassembly, reactive oxygen species (ROS) burst, asparagine metabolism, sugar transport, autophagy process, Ca2+ signaling, circadian clock response, brassinazole-resistant 1 (BZRI), and other stress cell signaling. A comprehensive understanding for the metabolic mechanism and regulatory network underlying N deficiency-induced leaf senescence may provide a theoretical guide to optimize the source-sink relationship during grain filling for the achievement of high yield by a selection of crop cultivars with the properly prolonged lifespan of functional leaves and/or by appropriate agronomic managements.
•Metabolic network and regulatory mechanism undrelying nitrogen deficiency-induced leaf senescence are comprehensively discussed.•Sugar acts as a key regulator for leaf senescence and root C/N ratio by connecting with hormone signaling and N metabolism.•Nitrogen deficiency-induced leaf senescence was closely associated with BRs-mediated autophagy and circadian clock response.
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