Summary: The dissolution of cotton fibres has been studied at different development stages before and after the onset of secondary wall deposition in solvents of varying quality. We show that the dissolution of the primary wall is inefficient even in good solvents. In moderately good solvents, the inside of the secondary wall dissolves by fragmentation, whereas the outside of the secondary wall swells. These data demonstrate the existence of a centripetal radial gradient in the dissolution capacity within the fibre, which must be related to age-dependent structural variation in the cell wall layers.

Six BnaProDH1 and two BnaProDH2 genes were identified in Brassica napus genome. The BnaProDH1 genes are mainly expressed in pollen and roots' organs while BnaProDH2 gene expression is associated with leaf vascular tissues at senescence. Proline dehydrogenase (ProDH) catalyzes the first step in the catabolism of proline. The ProDH gene family in oilseed rape (Brassica napus) was characterized and compared to other Brassicaceae ProDH sequences to establish the phylogenetic relationships between genes. Six BnaProDH1 genes and two BnaProDH2 genes were identified in the B. napus genome. Expression of the three paralogous pairs of BnaProDH1 genes and the two homoeologous BnaProDH2 genes was measured by real-time quantitative RT-PCR in plants at vegetative and reproductive stages. The BnaProDH2 genes are specifically expressed in vasculature in an age-dependent manner, while BnaProDH1 genes are strongly expressed in pollen grains and roots. Compared to the abundant expression of BnaProDH1, the overall expression of BnaProDH2 is low except in roots and senescent leaves. The BnaProDH1 paralogs showed different levels of expression with BnaA&C.ProDH1.a the most strongly expressed and BnaA&C.ProDH1.c the least. The promoters of two BnaProDH1 and two BnaProDH2 genes were fused with uidA reporter gene (GUS) to characterize organ and tissue expression profiles in transformed B. napus plants. The transformants with promoters from different genes showed contrasting patterns of GUS activity, which corresponded to the spatial expression of their respective transcripts. ProDHs probably have non-redundant functions in different organs and at different phenological stages. In terms of molecular evolution, all BnaProDH sequences appear to have undergone strong purifying selection and some copies are becoming subfunctionalized. This detailed description of oilseed rape ProDH genes provides new elements to investigate the function of proline metabolism in plant development.

In the framework of a gene flow assessment, we investigated the natural hybridization rate between Gossypium hirsutum (AADD genome) and G. herbaceum (AA genome). The latter species, a diploid progenitor of G. hirsutum, is spontaneously present in South Africa. Reciprocal crosses were performed without emasculation between G. herbaceum and G. hirsutum. Neither examination of the morphological characteristics nor flow cytometry analysis of the 335 plants resulting from the G. hirsutum × G. herbaceum cross showed any hybrid features. Of the 148 plants produced from the G. herbaceum × G. hirsutum cross, three showed a hybrid phenotype, and their hybrid status was confirmed by SSR markers. Analysis of DNA content by flow cytometry and morphological traits clearly showed that two of these plants were triploid (AAD). The third plant had a flow cytometry DNA content slightly higher than G. hirsutum. In addition, its morphological characteristics (plant architecture, presence and size of petal spots, leaf shape) led us to conclude that this plant was AAAD thus resulting from fertilization with an unreduced AA gamete of the female G. herbaceum parent. Fluorescent In Situ Hybridization (FISH) and meiotic behavior confirmed this hypothesis. To the best of our knowledge, this is the first description of such gametes in G. herbaceum, and it opens new avenues in breeding programs. Furthermore, this plant material could provide a useful tool for studying the expression of genes duplicated in the A and D cotton genome.