Lukens JH, Durbin RD. Tagetitoxin affects plastid development in seedling leaves of wheat.
PLANTA 1985;
165:311-321. [PMID:
24241135 DOI:
10.1007/bf00392227]
[Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/1984] [Accepted: 03/11/1985] [Indexed: 06/02/2023]
Abstract
Ultrastructural and biochemical approaches were used to investigate the mode of action of tagetitoxin, a nonhost-specific phytotoxin produced by Pseudomonas syringae pv. tagetis (Hellmers) Young, Dye and Wilkie, which causes chlorosis in developing - but not mature - leaves. Tagetitoxin has no effect on the growth rate or morphology of developing leaves of wheat (Triticum aestivum L.) seedlings. Its cytological effects are limited to plastid aberrations; in both light-and dark-grown leaves treated with toxin, internal plastid membranes fail to develop normally and plastid ribosomes are absent, whereas mitochondrial and cytoplasmic ribosomes are unaffected. The activity of a plastid stromal enzyme, ribulose-1,5-bisphosphate carboxylase (RuBPCase, EC 4.1.1.39), which is co-coded by nuclear and chloroplast genes, is markedly lower in extracts of both light-and dark-grown toxin-treated leaves, whereas the activity of another stromal enzyme, NADP-glyceraldehyde-3-phosphate dehydrogenase (NADP-G-3P-DH, EC 1.2.1.13), which is coded only by the nuclear genome, is significantly lower in extracts of light-grown, but not of dark-grown, treated leaves. The mitochondrial enzymes fumarase (EC 4.2.1.2) and cytochrome-c oxidase (EC 1.9.3.1) are unaffected by toxin in dark-grown leaves, but fumarase activity is reduced in light-grown ones. Four peroxisomal enzyme activities are lowered by toxin treatment in both light- and dark-grown leaves. Light- and dark-grown, toxintreated leaves contain about 50% and 75%, respectively, of the total protein of untreated leaves. There are threefold and twofold increases in free amino acids in light-grown and dark-grown treated leaves, respectively. In general, the effects of tagetitoxin are more extensive and exaggerated in light-grown than in dark-grown leaves. We conclude that tagetitoxin interferes primarily with a light-independent aspect of chloroplast-specific metabolism which is important in plastid biogenesis.
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