Richard J. Gladon

Lipoxygenase Is Involved in the Control of Potato Tuber Development

Plant lipoxygenases (LOXs) are a functionally diverse class of dioxygenases implicated in physiological processes such as growth, senescence, and stress-related responses. LOXs incorporate oxygen into their fatty acid substrates and produce hydroperoxide fatty acids that are precursors of jasmonic acid and related compounds. Here, we report the involvement of the tuber-associated LOXs, designated the Lox1 class, in the control of tuber growth. RNA hybridization analysis showed that the accumulation of Lox1 class transcripts was restricted to developing tubers, stolons, and roots and that mRNA accumulation correlated positively with tuber initiation and growth. In situ hybridization showed that Lox1 class transcripts accumulated in the apical and subapical regions of the newly formed tuber, specifically in the vascular tissue of the perimedullary region, the site of the most active cell growth during tuber enlargement. Suppression mutants produced by expressing antisense coding sequence of a specific tuber LOX, designated POTLX-1, exhibited a significant reduction in LOX activity in stolons and tubers. The suppression of LOX activity correlated with reduced tuber yield, decreased average tuber size, and a disruption of tuber formation. Our results indicate that the pathway initiated by the expression of the Lox1 class genes of potato is involved in the regulation of tuber enlargement.

Characterization of a cDNA encoding 5-aminolevulinic acid dehydratase in tomato (Lycopersicon esculentum Mill.)

SummaryA full-length cDNA clone encoding tomato (Lycopersicon esculentum Mill.) 5-aminolevulinic acid dehydratase (ALAD) was isolated and characterized. The primary structure predicts a 430-amino acid precursor which comprises a 41.7 kDa, 388-amino acid mature protein and a 47-amino acid transit sequence. The tomato primary sequence shows extensive homology to those of pea and spinach. Southern analysis indicated that 1 to 2 copies of the ALAD gene are present in the tomato genome. Northern blot analysis shows differential expression in various tomato organs, and constitutive developmental expression in tomato fruits.

Regulation of Glutamate-l-semialdehyde Aminotransferase Expression during Tomato (Lycopersicon esculentum Mill.) Fruit Development

Summary A full-length clone that encodes tomato fruit tissue ( Lycopersicon esculentum Mill. ‘Rutgers’) glutamate-1-semialdehyde aminotransferase (GSAT; EC 5.4.3.8) was isolated and characterized. Amino acid sequence analysis showed that the tomato GSAT clone exhibited a high level of homology to the amino acid sequences of corresponding GSAT proteins from other plant species. The primary structure of GSAT consists of a 481-amino acid precursor that includes a 46.7 kilounit (kU), 437-amino acid mature protein and a transit peptide of 44 amino acids. Southern analysis showed that a single copy of the GSAT gene was present in the tomato genome. Northern analysis showed that the abundance of GSAT transcripts declined throughout tomato fruit development and ripening. GSAT protein content decreased dramatically by 25 days postanthesis, and GSAT protein was undetectable by day 45, the approximate beginning of chlorophyll loss and carotenoid synthesis. These results show that GSAT is regulated developmentally at the level of transcript accumulation. In addition, posttranscriptional regulation may occur through decreased translation or increased degradation of GSAT protein.

Glutamic Acid and 5-Aminolevulinic Acid May Function as Precursors of System II Ethylene in Ripening Tomato Fruit

8 Introduction 9 Materials and Methods 11 Results 14 Discussion 16 Literature Cited 19 4. GENERAL SUMMARY AND CONCLUSIONS 27 ADDITIONAL LITERATURE CITED 29 ACKNOWLEDGMENTS 32

(Aminooxy)acetic acid inhibits petunia growth and gibberellin- and cytokinin-stimulated growth in bioassays

Abstract(Aminooxy)acetic acid (AOA) was applied to greenhouse-grown petunias and was used in bioassays for three plant growth hormones so that its growth regulator properties could be studied. In greenhouse studies foliar sprays of 4.8–12 mm AOA inhibited vegetative growth of petunia seedlings (Petunia xhybrida Vilm. ‘White Flash’). When gibberellin A 3 (GA3) was applied to shoot tips previously treated with AOA, plant growth was stimulated, but there was no AOA x GA3 interaction. Some changes in petunia leaf morphology induced by AOA were reversed by GA3. AOA inhibited elongation of corn coleoptile segments (Zea mays L. B73 x Mol7) whether or not 10 μm indole-3-acetic acid (IAA) was present, but there was no AOA x IAA interaction. AOA reduced lettuce hypocotyl (Lactuca sativa L. ‘Grand Rapids’) elongation induced by GA3 and radish cotyledon (Raphanus sativus L. ‘Champion’) expansion induced by benzyladenine (BA). We propose that AOA interferes with postsynthetic metabolism of plant hormones during cell elongation induced by GA3 and cell expansion induced by BA.

[Delta]-Aminolevulinic acid dehydratase activity during tomato fruit development and ripening

Introduction Materials and Methods Results Discussion Literature Cited 4. SUMMARY AND CONCLUSIONS LITERATURE CITED FOR GENERAL REVIEW OF LITERATURE ACKNOWLEDGEMENTS iii