closely if fruit yield is to be maximized. The first criterion to these processes is the natural development of organs in flowers and the continuous production of pollen with a high percentage of viability ( Eti, 1991 ; Griggs et al., 1971 ; Linskens
considered the importance of pollen development and morphology in clarifying the classification and identity of many plant species, e.g., peach [ Prunus persica (L.) Batsch], nectarine [ Prunus persica var. nectarina (Ait.) Maxim.], sweet cherry [ Prunus
Juglans regia L. is typical of Juglandaceae in that it is monoecious, wind-pollinated, and self-compatible. Despite its self-compatibility, breeding and research programs have encountered difficulties acquiring sufficient quantities of pollen
Vito S. Polito, Steven A. Weinbaum, and Tom T. Muraoka
Experiments were conducted to determine if differential responses of walnut pollen germination to temperature, previously observed to occur among genotypes, were genetically fixed or expressions of phenotypic plasticity representing adaptive responses to temperatures experienced during pollen development. Individual branches of a single walnut (Juglans regia L. cv. Serr) tree were warmed above ambient conditions during the final stages of pollen differentiation by directing a stream of moist, heated air into polyethylene enclosures, each containing an individual branch unit. Pollen was collected at staminate anthesis and incubated in germination medium on a temperature gradient apparatus. Model curves fitted to the in vitro pollen germination data were used to determine optimum germination temperatures. We found adaptive responses of pollen germination to temperatures experienced during pollen development. The optimum temperature for in vitro germination for pollen from branches maintained under ambient conditions was lower than that of pollen from branches with elevated temperature, and optimum germination temperature increased as a log function of integrated daily temperature (degree-days) experienced during pollen development.
P. Martínez-Gómez, T.M. Gradziel, E. Ortega, and F. Dicenta
Pollen of the California almond cultivars Nonpareil, Ne Plus Ultra, Sonora, and Peerless was evaluated for viability following storage over 12 months at 4, 0, -20, and -80 °C. The proportion of viable pollen exceeded 80% for all cultivars and for all temperatures evaluated after 2 months of storage. Following 12 months of storage at 4 °C, germination decreased to 8% for `Nonpareil', 10% for `Ne Plus Ultra', 50% for `Sonora', with no germination observed for `Peerless'. Storage at sub-freezing temperatures maintained pollen viability above 70% in `Nonpareil', `Ne Plus Ultra', and `Sonora' and above 40% in `Peerless'. Cultivars differed significantly in their tolerance to low temperature pollen storage. Within cultivars, differences in pollen germination following storage at 0, -20, or -80 °C were nonsignificant.
Jon T. Lindstrom, Chih-Hsien Lei, Michelle L. Jones, and William R. Woodson
Mature pollen from Petunia hybrida contains significant levels of 1-aminocyclopropane-1-carboxylic acid (ACC), and this ACC is thought to play a role in pollination-induced ethylene by the pistil. We investigated the developmental accumulation of ACC in anthers and pollen. The level of ACC in anthers was very low until the day before anthesis, at which time it increased 100-fold. A 1.1-kb partial ACC synthase cDNA clone (pPHACS2) was amplified from total RNA isolated from mature anthers by reverse transcriptase, followed by polymerase chain reaction using oligonucleotide primers synthesized to conserved amino acid sequences in ACC synthases. The expression of pPHACS2 mRNA during anther development was correlated with the accumulation of ACC and was localized to the pollen grain. The pPHACS2 cDNA was used to identify the PH-ACS2 gene from a library of genomic DNA fragments from Petunia hybrida. PH-ACS2 encoded an ACC synthase transcript of four exons interrupted by three introns. The ACC synthase protein encoded by the PH-ACS2 gene shared >80% homology with ACC synthases from tomato (LE-ACS3) and potato (ST-ACS1a). A chimeric PH-ACS2 promoter-β-glucuronidase (GUS) gene was used to transform petunia and transgenic plants were analyzed for GUS activity. GUS staining was localized to mature pollen grains and was not detected in other tissues. Despite similarities to LE-ACS3, we did not detect GUS activity under conditions of anaerobic stress or in response to auxin. A series of 5-prime-flanking DNA deletions revealed that sequences within the PH-ACS2 promoter were responsible for pollen-specific expression.
Josh H. Freeman, Stephen M. Olson, and Eileen A. Kabelka
Seedless watermelons account for 78% of the watermelons sold in the United States ( U.S. Department of Agriculture, 2006 ). Triploid watermelon plants do not produce sufficient viable pollen to pollenize themselves and a diploid cultivar must be
Guanxing Hu, Chao Gao, Xiaoming Fan, Wenfang Gong, and Deyi Yuan
Xenia is defined as the effect of foreign pollen on the development of fruit tissue. It involves the interaction between a nuclear gene from the male gamete and either two polar nuclear genes from the endosperm or one nuclear gene from the egg
Patrick J. Conner
pecan, breeding programs often must make use of stored pollen to achieve particular crosses. Efficient and reproducible viability testing is essential to facilitating the use of stored pollen because nut set cannot be determined until after the end of
Gaetano Distefano, Giuseppina Las Casas, Stefano La Malfa, Alessandra Gentile, Eugenio Tribulato, and Maria Herrero
when cultivated near other sexually compatible cultivars. To avoid seed formation, several strategies have been explored ( Vardi et al., 2008 ). Open pollination factors such as pollen flow ( Chao et al., 2005 ) or the pollination efficiencies of wind