Wild Brassica plants release seeds by a pod shattering mechanism; in related crop plants, such as oil‐seed rape, this can result in substantial loss of seed, and hence loss of revenue, and also in the distribution of seeds which can contaminate future crops and the environment. To identify strategies which may be used to reduce shatter, either by conventional breeding programmes or by genetic engineering, we have examined fruit development in oil‐seed rape (Brassica napus), and in the related B. juncea and Arabidopsis, using a combination of cytological, cytochemical and molecular techniques. We report here on the patterns of cellular differentiation and tissue development during fruit maturation, and suggest how this results in the shattering phenotype.
The movement of water in the dorsal region of the developing rice caryopsis was studied using solutions of the heavy metals lanthanum and uranium. In the electron microscope electron-opaque deposits were confined to the cell walls of the pigment strand indicating that this is the main route for the water which enters and leaves the caryopsis during grain filling. The pathway of assimilates into the developing caryopsis was examined using isolated caryopses which had taken up solutions of fluorescent dyes and also by autoradiography of caryopses which had transported (14)C-labelled assimilates in vivo. The results show that assimilates unloaded from the phloem move through the pigment strand and circumferentially via cells of the nucellus before entering the endosperm. A scheme is presented for the interrelations of water and assimilate transport during grain filling.
Assimilates entering the developing rice caryopsis traverse a short-distance pathway between the terminal sieve elements of the pericarp vascular bundle and the aleurone layer. The ultrastructure of this pathway has been studied. Sieve elements in the pericarp vascular bundle are smaller than their companion cells.The sieve elements show few connections with surrounding vascular parenchyma elements but are connected to companion cells by compound plasmodesmata. Companion cells, in turn, are connected to vascular parenchyma elements by numerous compound plasmodesmata present in wall thickenings. Assimilates leaving the sieve element - companion cell complex must laterally traverse cells of the pigment strand before they come into contact with the aleurone layer. The pigment strand cells have modified inner walls made up of a suberin-like material. This material may act as a permeability barrier isolating the apoplast from the symplast of the pigment strand. The walls of the pigment strand cells are traversed by numerous plasmodesmata. Water may be conducted to the endosperm through the isolated cell-wall system of the pigment strand while assimilates possibly move via plasmodesmata. High frequencies of plasmodesmata occur at the junction between the pigment strand and the nucellus and also between adjacent cells of the nucellus. By contrast, plasmodesmata are absent between the nucellus and the aleurone layer and also between the nucellus and the seed coat. A predominantly circumferential and symplastic transport pathway is likely between the pigment strand and nucellus. In view of the total absence of plasmodesmata between the nucellus and the aleurone layer assimilates entering the endosperm may have to cross the plasmalemma of the nucellus. It is possible that constraints to the flow of assimilates may occur in the short-distance pathway between the terminal sieve element - companion cell complexes and the endosperm, and this is discussed.
There are several reports of the association among lentil characters based on a few, relatively similar lines grown in single environments. Their results have often been inconsistent because of inadequate sampling of genotypes and environments. This study examined associations between economic characters in lentil over a wide range of genetic material and environments in West Asia. The first part of the study concerned correlations within large samples from the world lentil collection grown in two seasons, and the second part covered a smaller sample of genetic material from the collection sown over a wider range of conditions.The results showed similar phenotypic correlations over two seasons, contrasting in rainfall, in the world lentil collection. Similar genetic and phenotypic correlations were also shown by the smaller sample of germplasm over 10 environments. These results indicated low importance of covariance due to environmental and genotype-environment interaction effects. Seed yield was positively correlated with straw yield, indicating selection for either character will increase the other trait. The correlation between seed protein content and seed yield was small and negative, while the correlation of protein with straw yield was positive in sign. This suggests that the current ICARDA goals of selection for high seed and straw yield will not have a major correlated effect on seed protein content. There was a strong positive correlation between seed size and cooking time (r = 0.96), therefore seed size can be used to predict cooking time.
The results of studies on assimilate and water transport in the developing caryopsis of rice are summarised . Evidence is presented for a symplastic movement of solutes as far as the aleurone layer . However, transport into the apoplast at the nucellus/aleurone interface appears to be a necessary step due to the absence of plasmodesmata at this site. It is suggested that water leaves the caryopsis during grain filling by the isolated cell walls of the pigment strand, the suberised walls of these cells functioning to isolate the apoplast from the symplast and thereby allowing opposing fluxes of water and assimilates to occur in the dorsal region of the grain .
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