Calcium dynamics in tomato pollen tubes using the Yellow Cameleon 3.6 sensor.

KEY MESSAGE: In vitro tomato pollen tubes show a cytoplasmic calcium gradient that oscillates with the same period as growth. Pollen tube growth requires coordination between the tip-focused cytoplasmic calcium concentration ([Ca2+]cyt) gradient and the actin cytoskeleton. This [Ca2+]cyt gradient is necessary for exocytosis of small vesicles, which contributes to the delivery of new membrane and cell wall at the pollen tube tip. The mechanisms that generate and maintain this [Ca2+]cyt gradient are not completely understood. Here, we studied calcium dynamics in tomato (Solanum lycopersicum) pollen tubes using transgenic tomato plants expressing the Yellow Cameleon 3.6 gene under the pollen-specific promoter LAT52. We use tomato as an experimental model because tomato is a Solanaceous plant that is easy to transform, and has an excellent genomic database and genetic stock center, and unlike Arabidopsis, tomato pollen is a good system to do biochemistry. We found that tomato pollen tubes showed an oscillating tip-focused [Ca2+]cyt gradient with the same period as growth. Then, we used a pharmacological approach to disturb the intracellular Ca2+ homeostasis, evaluating how the [Ca2+]cyt gradient, pollen germination and in vitro pollen tube growth were affected. We found that cyclopiazonic acid (CPA), a drug that inhibits plant PIIA-type Ca2+-ATPases, increased [Ca2+]cyt in the subapical zone, leading to the disappearance of the Ca2+ oscillations and inhibition of pollen tube growth. In contrast, 2-aminoethoxydiphenyl borate (2-APB), an inhibitor of Ca2+ released from the endoplasmic reticulum to the cytoplasm in animals cells, completely reduced [Ca2+]cyt at the tip of the tube, blocked the gradient and arrested pollen tube growth. Although both drugs have antagonistic effects on [Ca2+]cyt, both inhibited pollen tube growth triggering the disappearance of the [Ca2+]cyt gradient. When CPA and 2-APB were combined, their individual inhibitory effects on pollen tube growth were partially compensated. Finally, we found that GsMTx-4, a peptide from spider venom that blocks stretch-activated Ca2+ channels, inhibited tomato pollen germination and had a heterogeneous effect on pollen tube growth, suggesting that these channels are also involved in the maintenance of the [Ca2+]cyt gradient. All these results indicate that tomato pollen tube is an excellent model to study calcium dynamics.

The effect of three plant bioregulators on pollen germination, pollen tube growth and fruit set in almond [Prunus dulcis (Mill.) D.A. Webb] cvs. Non Pareil and Carmel

Background In commercial almond [Prunus dulcis (Mill.) D.A. Webb] orchards in Chile, the percentage of fruit set is low and commonly reaches 5–30%. As almond trees bloom during a cool period and also suffer from self-incompatibility, any factor that can improve pollination, pollen germination and pollen tube growth or extend the effective pollination period, such as the application of plant bioregulators (PBRs), should be beneficial for fruit production. Results Three plant bioregulators (PBRs): brassinolide (BL), gibberellic acid (GA3) and kinetin (KN) were evaluated for pollen germination and pollen tube growth in vitro, as well as for fruit set in almond cultivars Non Pareil and Carmel, in central Chile, during the 2013 and 2014 seasons. For pollen germination in vitro, the BL concentration of 10 mg L- 1 had the highest value in Non Pareil (97.7%), after 4 h germination in 2014 growing season (the control was 90.9%). KN at a concentration of 50 µL L- 1 induced the longest pollen tube growth of 1243.4 µm in Carmel after 8 h germination in 2013 (the control was 917.7 µm). In Non Pareil, the highest percentage of fruit set (31.0%) was achieved in 2014 by spraying during bloom at pink bud stage with KN at 50 µL L- 1 (the control was 16.7%). Conclusions A significant favorable effect of the tested PBRs was observed in pollen germination and pollen tube growth in vitro, as well as on fruit set in Non Pareil and Carmel almonds.

Negative effects of heterospecific pollen receipt vary with abiotic conditions: ecological and evolutionary implications.

BACKGROUND AND AIMS: Studies that have evaluated the effects of heterospecific pollen (HP) receipt on plant reproductive success have generally overlooked the variability of the natural abiotic environment in which plants grow. Variability in abiotic conditions, such as light and water availability, has the potential to affect pollen-stigma interactions (i.e. conspecific pollen germination and performance), which will probably influence the effects of HP receipt. Thus, a more complete understanding of the extent, strength and consequences of plant-plant interactions via HP transfer requires better consideration of the range of abiotic conditions in which these interactions occur. This study addresses this issue by evaluating the effects of two HP donors (Tamonea curassavica and Angelonia angustifolia) on the reproductive success of Cuphea gaumeri, an endemic species of the Yucatan Peninsula. METHODS: Mixed (conspecific pollen and HP) and pure (conspecific pollen only) hand-pollinations were conducted under varying conditions of water and light availability in a full factorial design. Reproductive success was measured as the number of pollen tubes that reached the bottom of the style. KEY RESULTS: Only one of the two HP donors had a significant effect on C. gaumeri reproductive success, but this effect was dependent on water and light availability. Specifically, HP receipt caused a decrease in pollen tube growth, but only when the availability of water, light or both was low, and not when the availability of both resources was high. CONCLUSIONS: The results show that the outcome of interspecific post-pollination interactions via HP transfer can be context-dependent and vary with abiotic conditions, thus suggesting that abiotic effects in natural populations may be under-estimated. Such context-dependency could lead to spatial and temporal mosaics in the ecological and evolutionary consequences of post-pollination interactions.