Analysis of the reproduction mode in Psidium spp. using the pollen:ovule ratio

This research aimed to explore the reproductive characteristics of three species of Psidium (P. guajava L., P. cattleyanum Sabine, and P. guineense Sw.) and estimate a probable reproduction strategy based on the pollen:ovule (P:O) methodology. The number of pollen grains per floral bud (NGPB), number of pollen grains per anther (NGPA), number of anthers per flower bud (NAB), number of ovules per flower bud (NOB), and the P:O ratio of each species were estimated. All species had a P:O ratio over 2,000 and were classified as xenogamous. P.guajava presented the highest values for all characteristics evaluated, with the NGPB at 3,777,519, the NOB at 584.50 and a P:O ratio of 6,462.82. Similarly, P. cattleyanum had a P:O ratio of 5,649.89 (NGPB 762,736 and NOB 135). However, P. guineense was considered facultative xenogamous, with P:O of 2,085.75, the NGPB at 741,484 and the NOB at 355.50. Thus, it was concluded that the studied species have a preference for allogamy and require many pollen grains to fertilize each ovule, demonstrating that the transfer of pollen to the stigma is not very specialized.

Preferential reproduction mode of hermaphrodite papaya plant (Carica papaya L; Caricaceae)

This research was done to study the reproductive system of papaya hermaphrodite plant based on the histochemical nature of pollen grain, stigma receptivity, in vivo pollen grain germination and pollen:ovule ratio. In the histochemical analysis, pollen grains were stained by using Sudan IV and I2KI solution ; the stigma receptivity was assessed by alpha-naphthtyl acetate solution in closed and opened flowers. Pollen germination and pollen tube growing were examined in flower buds near anthesis with 0.1% aniline blue. To estimate the pollen:ovule ratio , anthers from each flower bud were dissected and all pollen grains were counted; ovules were dissected from ovaries and were counted under stereomicroscope. The results indicated that papaya pollen grains are of lipidic nature; the stigmas were receptive before the opening and until 48 hours after opening; the pollen grains germinated and emitted polinic tube before flower opening and the pollen:ovule ratio indicated the predominance of autogamous reproductive system. These results indicate that hermaphrodite papaya trees is preferentially of optional autogamous with cleistogamy.

Does pollen abortion increase with plant age?

The large tropical forest tree, Anacardium excelsum (Bertero & Balb. Ex Kunth) Skeels, of the family Anacardiaceae, was studied in Panama. Using Alexander’s stain, which differentiates aborted and non-aborted pollen, the proportion of aborted pollen versus plant age, size variation in aborted and non-aborted pollen and pollen:ovule ratio were estimated. Aborted pollen was smaller than non-aborted pollen regardless of plant age. The proportion of aborted pollen varied from 15.8 to 54.7% showing a steady increase with plant age, and the pollen:ovule ratio also increased with age. These results support the qualitative prediction that pollen abortion gradually increases with ageing reflecting an increase in genetic load with age. Key words: Age effect, reproductive success, tropical forest

Self-Incompatibility, Protandry, Pollen Production and Pollen Longevity in Banksia menziesii

Controlled self- and cross-pollination indicated that a natural population of Banksia menziesii (Proteaceae) was self-incompatible. Flowers were protandrous. Deposition of pollen into the stigmatic cavity was regulated by opening of the stigmatic groove. Stigmatic grooves opened 24-48 h after the flowers opened. Pollen production was high and the pollen:ovule ratio was approximately 10000. Over 90% of pollen grains were viable when flowers first opened. Viability decreased rapidly with time and most pollen was inviable within 24 h. These results indicate that B. menziesii requires pollen vectors to produce seed and suggest that pollinators may have influenced the evolution of the reproductive traits that were examined.