Homogeneous populations of developing microspores and pollen from anthers of lily (Lilium longiflorum Thumb.) and tobacco (Nicotiana tabacum L.) show a continuous production of biomass, reaching a maximum in young pollen. The rate of RNA synthesis was 460 fg · h(-1) in young binucleate cells, 138 fg · h(-1) in late binucleate cells and 56 fg · h(-1) in microspores. The mRNA population in developing pollen can be separated into three groups. In the first group, certain types of mRNAs are present at a constant level during all stages of development. A second group is characteristic of young pollen and increases quantitatively until anthesis. A third group is seen transiently; to this belong mRNAs present only before mitosis or at a distinct cell stage after mitosis. Some of the translation products of this latter group of mRNAs showed similarities between lily and tobacco on two-dimensional gels in respect of molecular weight and isolectric point, indicating that those mRNAs and proteins play a role in the regulation of pollen development.

Transcripts of the ntp303 gene accumulate abundantly throughout pollen development, whereas the protein only accumulates to detectable levels after pollen germination. In an attempt to explain the divergence in the accumulation profiles of the mRNA and the protein, we investigated the role of the untranslated regions (UTRs) in enhancing ntp303 translation during the transition from developing to germinating pollen. Luciferase reporter gene fusion constructs containing the ntp3035′-UTR gave rise to luciferase activity that was up to 60-fold higher during pollen tube growth than that of constructs containing different 5′-UTRs. No apparent differences in the luciferase activity of these constructs were observed during pollen development. Thentp303 5′-UTR-mediated increase in luciferase activity was not significantly influenced by coding region or 3′-UTR sequences. Furthermore, enhanced luciferase activity directed by thentp303 5′-UTR occurred predominantly at the post-transcriptional level. A series of 5′-UTR deletion constructs was created to identify putative regulatory sequences required for the high level of translation during pollen tube growth. Two predicted stem loop structures (H-I and H-II) caused a complete inhibition of the enhanced translation after their total or partial deletion. A (GAA)8repeat within the H-I stem loop structure was demonstrated to be important for the modulation of translation efficiency. The H-II stem loop structure was found to be essential for the determination of mRNA stability.

SummaryThe regulation of flavonol biosynthesis was studied in anthers and pistils of Solanum tuberosum.

No abstract

In a program aimed at studying genes ex-ly few data have been obtained that shed light on the mopressed in pistils, the cDNA clone STS 15 was isolated lecular basis of a successful pollen-pistil interaction, from a cDNA library of pollinated pistils of Solanum tu-Such an interaction is characterized by germination and berosum and was found to be expressed only in pistils. During development of the pistil, the accumulation of STS 15 transcripts, which are 0.7 kb long, reached a max imum just before anthesis and declined in fully open flowers. Southern blot analysis revealed that stslS was present as a small gene family in dihaploid potato. In situ hybridization experiments indicated that STS15 was strongly expressed in the cortex of the style and at a low level in the stigma. No hybridization signal was observed in the transmitting tissue. The temporal and spatial ex pression patterns of STS 15 indicate that the gene prod ucts of the stslS gene might be involved in the function of the stylar cortex or in making the pistil competent for pollination.

A gene, sts14, coding for a highly expressed mRNA in pistils of Solanum tuberosum, was isolated. Northern blot and in situ analyses demonstrated that the gene was expressed throughout pistil development in both the stylar cortex and the stigma. The deduced STS14 protein displays similarity to the pathogenesis-related PR-1 proteins. A possible function for protection or guidance of the pollen tubes through the pistil is discussed.

No abstract

The effect of elevated temperatures on protein synthesis in pollen from Petunia hybrida and Lilium longiflorum was investigated and compared with their effect in root-tissue tissue of Petunia. The results demonstrate that the incorporation of [35-S] methionine into protein does not change in pollen incubated at temperatures up to 40°C, but decreased with 65% at 45°C as compared to incorporation at 27"e.The qualitative changes that occurred for the proteins synthesized at 2r and 40°C were not identical for pollen from Petunia and Lilium. The proteins synthesized at 27°and 40°C were very similarwithin one species. None of the changes in proteins synthesized at 40°C in pollen showed anycorrelation with heat shock proteins formed in rootlets from Petunia.