Pollen performance, cell number, and physiological state in the early-divergent angiosperm Annona cherimola Mill. (Annonaceae) are related to environmental conditions during the final stages of pollen development

Abstract

Pollen performance is an important determinant for fertilization success, but high variability in pollen behavior both between and within species occurs in different years and under varying environmental conditions. Annona cherimola, an early-divergent angiosperm, is a species that releases a variable ratio of bicellular and tricellular hydrated pollen at anther dehiscence depending on temperature. The presence of both bi- and tricellular types of pollen is an uncommon characteristic in angiosperms and makes Annona cherimola an interesting model to study the effect of varying environmental conditions on subsequent pollen performance during the final stages of pollen development. In this work, we study the influence of changes in temperature and humidity during the final stages of pollen development on subsequent pollen performance, evaluating pollen germination, presence of carbohydrates, number of nuclei, and water content. At 25 °C, which is the average field temperature during the flowering period of this species, pollen had a viability of 60-70 %, starch hydrolyzed just prior to shedding, and pollen mitosis II was taking place, resulting in a mixture of bi- and tricellular pollen. This activity may be related to the pollen retaining 70 % water content at shedding. Temperatures above 30 °C resulted in a decrease in pollen germination, whereas lower temperatures did not have a clear influence on pollen germination, although they did have a clear effect on starch hydrolysis. On the other hand, slightly higher dehydration accelerated mitosis II, whereas strong dehydration arrested starch hydrolysis and reduced pollen germination. These results show a significant influence of environmental conditions on myriad pollen characteristics during the final stages of pollen development modifying subsequent pollen behavior and contributing to our understanding of the variability observed in pollen tube performance.

Repeated evolution of tricellular (and bicellular) pollen

“…All but four of the variable speeies are from genera or families that are also polymorphic at the intrageneric or intrafamilial levels, respeetively, suggesting that the different rates of evolution found in the HRM analyses extend to the intraspecifie level. The exception that proves the rule is the work of Lora et al (2009Lora et al ( , 2012 on temperature-and phenology-dependent variation in Annona cherimola. This speeies is in the almost eompletely bieellular eumagnoliid elade (Fig.…”

The Trials and Tribulations of the Plant Male Gametophyte — Understanding Reproductive Stage Stress Tolerance

“…When this occurs (e.g. Annona cherimola), the ratio between bi-cellular and tri-cellular pollen grains was shown to depend on environmental factors such as temperature regime and relative humidity during the last phases of maturation [32]. Tri-cellular pollen grains have completed their development before dispersal and are typical for plant families that include important dicot and monocot crop species such as Asteraceae, Lamiaceae, Brassicaceae and Poaceae (Table 1).…”

“…The size and shape of pollen grains, together with the events in the anther wall regulating dehiscence all collaborate to determine desiccation time, pollen viability and pollination success (Tables 6 and 7). Variation in relative air humidity, together with abiotic stresses that affect relative humidity (heat, drought, cold stress), cause problems with pollen presentation, anther opening, dehiscence [276,277] and pollen tube growth [32]. Precocious germination while still in the anther [278,279], or while waiting for a pollinator to disperse the pollen ( Figure 3E) [280,281], is due to inappropriate levels of humidity.…”

Reproductive Biology of Mango (Mangifera Indica) in a Mediterranean Climate

“…Similar results were observed by Sukhvibul et al (2000) for `Kensington´. Further work on the temperatures, not only during pollen germination, but also during pollen development may shed light on these differences, as it occurs in other species as cherimoya (Lora et al, 2012), in which temperature in the final stages of pollen development has a reflection on the subsequent pollen performance.…”