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Cell wall polysaccharide biosynthesis and related metabolism in elicitor-stressed cells of French bean (Phaseolus vulgaris L.).

ABSTRACT: Enzyme activities involved in quantitative and qualitative flux of sugars into cell wall polysaccharides were determined following elicitor treatment of suspension cultured cells of French bean (Phaseolus vulgaris L.). Two subsets of activities were examined: the first were involved in synthesis and metabolism of UDP-glucose and the provision of the pool of UDP-sugars, and the second a selection of membrane-bound glycosyltransferases involved in the synthesis of pectins, hemicelluloses and glucans of the primary cell wall. Of the first group, only UDP-glucose dehydrogenase (EC 1.1.1.22) showed any significant induction in response to elicitor treatment, sucrose synthase (EC 2.4.1.13), UDP-glucuronate decarboxylase (EC 4.1.1.35), UDP-glucose and UDP-xylose 4-epimerases (EC 5.1.3.2 and EC 5.1.3.5 respectively) did not change in activity significantly over the time course. In contrast, enzymes of the second group showed a more complex response. Callose synthase (glucan synthase II, EC 2.4.1.12) increased in activity, as has been shown in other systems, while arabinan synthase (EC 2.4.1.-), xylan synthase (EC 2.4.1.72), xyloglucan synthase (EC 2.4.1.72) and glucan synthase I (EC 2.4.1.12) activities were rapidly depleted from membranes within 3 h following elicitor action. This rapid turnover of activity was striking, indicating that the half-life of such enzymes can be short and that elicitor action causes substantial perturbation of some membrane activities. Glucan synthase I activity appears to increase in the later stages over the time period measured, indicating some recovery of this metabolism.

SUBMITTER: Robertson D

PROVIDER: S-EPMC1136584 | biostudies-other | 1995 Mar

REPOSITORIES: biostudies-other

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Project description:Common bean (Phaseolus vulgaris L.) is a staple food in Brazil with both nutritional and socioeconomic importance. As an orphan crop, it has not received as much research attention as the commodity crops. Crop losses are strongly related to virus diseases transmitted by the whitefly Bemisia tabaci, one of the most important agricultural pests in the world. The main method of managing whitefly-transmitted viruses has been the application of insecticides to reduce vector populations. Compared to chemical vector control, a more sustainable strategy for managing insect-borne viruses is the development of resistant/tolerant cultivars. RNA interference has been applied to develop plant lines resistant to the whitefly in other species, such as tomato, lettuce and tobacco. Still, no whitefly-resistant plant has been made commercially available to date. Common bean is a recalcitrant species to in vitro regeneration; therefore, stable genetic transformation of this plant has been achieved only at low frequencies (<1%) using particle bombardment. In the present work, two transgenic common bean lines were obtained with an intron-hairpin construct to induce post-transcriptional gene silencing against the B. tabaci vATPase (Bt-vATPase) gene, with stable expression of siRNA. Northern blot analysis revealed the presence of bands of expected size for siRNA in leaf samples of the line Bt-22.5, while in the other line (11.5), the amount of siRNA produced was significantly smaller. Bioassays were conducted with both lines, but only the line Bt-22.5 was associated with significant mortality of adult insects (97% when insects were fed on detached leaves and 59% on the whole plant). The expression of the Bt-vATPase gene was 50% lower (p < 0.05) in insects that fed on the transgenic line Bt-22.5, when compared to non-transgenic controls. The transgenic line did not affect the virus transmission ability of the insects. Moreover, no effect was observed on the reproduction of non-target organisms, such as the black aphid Aphis craccivora, the leafminer Liriomyza sp. and the whitefly parasitoid Encarsia formosa. The results presented here serve as a basis for the development of whitefly-tolerant transgenic elite common bean cultivars, with potential to contribute to the management of the whitefly and virus diseases.

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Cell wall polysaccharide biosynthesis and related metabolism in elicitor-stressed cells of French bean (Phaseolus vulgaris L.).

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