Reactive oxygen species (ROS) produced by NAD(P)H oxidases play a central role in plant stress responses and development. To better understand the function of NAD(P)H oxidases in plant development, ...we characterized the Arabidopsis thaliana NAD(P)H oxidases RBOHH and RBOHJ. Both proteins were specifically expressed in pollen and dynamically targeted to distinct and overlapping plasma membrane domains at the pollen tube tip. Functional loss of RBOHH and RBOHJ in homozygous double mutants resulted in reduced fertility. Analyses of pollen tube growth revealed remarkable differences in growth dynamics between Col–0 and rbohh–1 rbohj–2 pollen tubes. Growth rate oscillations of rbohh–1 rbohj–2 pollen tubes showed strong fluctuations in amplitude and frequency, ultimately leading to pollen tube collapse. Prior to disintegration, rbohh–1 rbohj–2 pollen tubes exhibit high‐frequency growth oscillations, with significantly elevated growth rates, suggesting that an increase in the rate of cell‐wall exocytosis precedes pollen tube collapse. Time‐lapse imaging of exocytic dynamics revealed that NAD(P)H oxidases slow down pollen tube growth to coordinate the rate of cell expansion with the rate of exocytosis, thereby dampening the amplitude of intrinsic growth oscillations. Using the Ca²⁺ reporter Yellow Cameleon 3.6, we demonstrate that high‐amplitude growth rate oscillations in rbohh–1 rbohj–2 pollen tubes are correlated with growth‐dependent Ca²⁺ bursts. Electrophysiological experiments involving double mutant pollen tubes and pharmacological treatments also showed that ROS influence K⁺ homeostasis. Our results indicate that, by limiting pollen tube growth, ROS produced by NAD(P)H oxidases modulate the amplitude and frequency of pollen tube growth rate oscillations.
The objective of this study is to examine 2016 data to compare airborne Morus and Olea pollen concentrations at five stations in the metropolitan area of Las Vegas and one in the Mojave Desert, to ...determine any differences between microenvironments. The results at the Mojave site suggest pollen transport is limited to the metropolitan area.
The establishment of pollen–pistil compatibility is strictly regulated by factors derived from both male and female reproductive structures. Highly diverse small cysteine-rich proteins (CRPs) have ...been found to play multiple roles in plant reproduction, including the earliest stages of the pollen–stigma interaction. Secreted CRPs found in the pollen coat of members of the Brassicaceae, the pollen coat proteins (PCPs), are emerging as important signalling molecules that regulate the pollen–stigma interaction.
Using a combination of protein characterization, expression and phylogenetic analyses we identified a novel class of Arabidopsis thaliana pollen-borne CRPs, the PCP-Bs (for pollen coat protein B-class) that are related to embryo surrounding factor (ESF1) developmental regulators. Single and multiple PCP-B mutant lines were utilized in bioassays to assess effects on pollen hydration, adhesion and pollen tube growth.
Our results revealed that pollen hydration is severely impaired when multiple PCP-Bs are lost from the pollen coat. The hydration defect also resulted in reduced pollen adhesion and delayed pollen tube growth in all mutants studied.
These results demonstrate that AtPCP-Bs are key regulators of the hydration ‘checkpoint’ in establishment of pollen–stigma compatibility. In addition, we propose that interspecies diversity of PCP-Bs may contribute to reproductive barriers in the Brassicaceae.
Pollen tube growth is an essential aspect of plant reproduction because it is the mechanism through which nonmotile sperm cells are delivered to ovules, thus allowing fertilization to occur. A pollen ...tube is a single cell that only grows at the tip, and this tip growth has been shown to depend on actin filaments. It is generally assumed that myosin-driven movements along these actin filaments are required to sustain the high growth rates of pollen tubes. We tested this conjecture by examining seed set, pollen fitness, and pollen tube growth for knockout mutants of five of the six myosin XI genes expressed in pollen of Arabidopsis (Arabidopsis thaliana). Single mutants had little or no reduction in overall fertility, whereas double mutants of highly similar pollen myosins had greater defects in pollen tube growth. In particular,myo11c1
myo11c2pollen tubes grew more slowly than wild-type pollen tubes, which resulted in reduced fitness compared with the wild type and a drastic reduction in seed set. Golgi stack and peroxisome movements were also significantly reduced, and actin filaments were less organized inmyo11c1
myo11c2pollen tubes. Interestingly, the movement of yellow fluorescent protein-RabA4d-labeled vesicles and their accumulation at pollen tube tips were not affected in themyo11c1
myo11c2double mutant, demonstrating functional specialization among myosin isoforms. We conclude that class XI myosins are required for organelle motility, actin organization, and optimal growth of pollen tubes.
Calcium, as a ubiquitous second messenger, plays essential roles in tip-growing cells, such as animal neurons, plant pollen tubes, and root hairs. However, little is known concerning the regulatory ...mechanisms that code and decode Ca2+ signals in plants. The evidence presented here indicates that a calcium-dependent protein kinase, CPK32, controls polar growth of pollen tubes. Overexpression of CPK32 disrupted the polar growth along with excessive Ca2+ accumulation in the tip. A search of downstream effector molecules for CPK32 led to identification of a cyclic nucleotide-gated channel, CNGC18, as an interacting partner for CPK32. Co-expression of CPK32 and CNGC18 resulted in activation of CNGC18 in Xenopus oocytes where expression of CNGC18 alone did not exhibit significant calcium channel activity. Overexpression of CNGC18 produced a growth arrest phenotype coupled with accumulation of calcium in the tip, similar to that induced by CPK32 overexpression. Co-expression of CPK32 and CNGC18 had a synergistic effect leading to more severe depolarization of pollen tube growth. These results provide a potential feed-forward mechanism in which calcium-activated CPK32 activates CNGC18, further promoting calcium entry during the elevation phase of Ca2+ oscillations in the polar growth of pollen tubes.
This study identified a molecular link between calcium-dependent protein kinase (CPK32) and Ca2+-permeable channel (CNGC18) in control of pollen tube tip growth, implicating a feed-forward mechanism in the formation of the tip-focused Ca2+ gradient through the CPK32–CNGC18 signaling pathway.
Summary
While changes in the transcriptome and proteome of developing pollen have been investigated in tobacco and other species, the metabolic consequences remain rather unclear. Here, a broad range ...of metabolites was investigated in close succession of developmental stages. Thirteen stages of tobacco male gametophyte development were collected, ranging from tetrads to pollen tubes. Subsequently, the central metabolome and sterol composition were analyzed by GC‐mass spectrometry (MS), monitoring 77 metabolites and 29 non‐identified analytes. The overall results showed that development and tube growth could be divided into eight metabolic phases with the phase including mitosis I being most distinct. During maturation, compounds such as sucrose and proline accumulated. These were degraded after rehydration, while γ‐aminobutyrate transiently increased, possibly deriving from proline breakdown. Sterol analysis revealed that tetrads harbor similar sterols as leaves, but throughout maturation unusual sterols increased. Lastly, two further sterols exclusively accumulated in pollen tubes. This study allows a deeper look into metabolic changes during the development of a quasi‐single cell type. Metabolites accumulating during maturation might accelerate pollen germination and tube growth, protect from desiccation, and feed pollinators. Future studies of the underlying processes orchestrating the changes in metabolite levels might give valuable insights into cellular regulation of plant metabolism.
Significance Statement
This study presents a primary metabolite map of 13 developmental stages of tobacco male gametophytes ranging from tetrads to mature pollen, rehydrated pollen and pollen tubes. The close succession of the monitored developmental stages demonstrated that the metabolite pattern changes sharply several times, especially during mitosis I and during rehydration.
PDF
