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.
A. F. Iezzoni and A. M. Hancock
Pollen samples from 4 sour cherry (Prunus cerasus L.) and 13 sweet cherry (P. avium L.) cultivars were examined by scanning electron microscopy (SEM). Pollen size did not differ significantly between species or ploidy level. Variability in size both within and among cultivars was greater in sour cherry than in sweet cherry. Giant pollen grains occurred in a low frequency in both sweet and sour cherry, equatorial diameter being responsible for the increased size.
E. Pimienta, V.S. Polito, and D.E. Kester
Investigation of pollen grain germination and retention on the stigma, and pollen tube frequency in the style following compatible (cross) and incompatible (self) pollinations in ‘Nonpareil’ almond [Prunus dulcis (Mill.) D.A. Webb Syn. Prunus amygdalus Batsch.J revealed that rejection of incompatible male gametophytes occurs on the stigma as well as in the style. Self-pollinations are characterized by lower pollen grain retention on the stigma, reduced and delayed pollen germination, and, where pollen germination had occurred, a low frequency of pollen tubes growing through the style. Pollen tube growth slowed greatly after the tubes entered the ovarian locule before they reached the ovule.
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.
M. H. Dickson and M. A. Boettger
Pollen germination in vivo in beans (Phaseolus vulgaris L.) was less at 8° and 12°C than at 18°. There were large cultivar differences, and germination at 9 am was no different from that at 3 pm. Pollen from bean flowers grown in the greenhouse at 21° Day/18°C Night (D/N) was transferred to plants in bloom at combinations of 8°, 10°, and 12° N, and 20°, 25°, and 30° D. Pollen from plants at the 9 temperature combinations also was used to pollinate plants in the greenhouse. Pollen from plants grown at 30° as compared to 20° and 25°, resulted in reduced seed yields. Conversely, viable pollen transferred to plants at 30° reduced set insignificantly. Thirty/8° D/N combinations resulted in the lowest yields. Low night temperatures appeared to inhibit ovule viability. In contrast, high temperatures reduced pollen viability. NY 5-161 and OSU 1604 were more stable than BBL 47, BBL 92, and PI 165426 at both high and low temperatures.
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.
Brent Tisserat and Darleen A. DeMason
Pollen samples of 4 cultivars and clones of Phoenix dactylifera L., 2 clones of P. reclinata Jacq. and one clone each of P. humilis Royle, P. roebelenii O’Brien × P. paludosa Roxb., P. rupicola T. Anderson and P. sylvestris (L.) Roxb. were compared using the scanning electron microscope (SEM). All grains were monosulcate, elliptical, and had tectate-perforate exines. Cultivars could be distinguished by differences in pollen morphology and exine structure. Characters that showed morphological variation included presence or absence of wax-like substances, grain length, grain width, and grain length:width ratio. Diverse structural characteristics included shape, pattern, size, and frequency of tectal perforations. Morphological and structural characteristics of pollen may serve as an aid in the taxonomic identification of staminate cultivars in Phoenix.