Biomedical subjects

Todd E Young

Publications and source records attributed to Todd E Young.

3 recordsLinked to original sources

PubMed2004

Senescence-induced expression of cytokinin reverses pistil abortion during maize flower development.

Maize is a monoecious species that produces imperfect (unisexual), highly derived flowers called florets. Within the spikelet, the basic repeating unit of the maize inflorescence, the spikelet meristem gives rise to an upper and a lower floret. Although initially bisexual, floret unisexuality is established through selective organ elimination. In addition, the lower floret of each ear spikelet is aborted early in its development, leaving the upper floret to mature as the only pistillate floret. Expression from the cytokinin-synthesizing isopentenyl transferase (IPT) enzyme under the control of the Arabidopsis senescence-inducible promoter SAG (senescence associated gene)12 was observed during early maize floret development. Moreover, the lower floret was rescued from abortion, resulting in two functional florets per spikelet. The pistil in each floret was fertile, but the spikelet produced just one kernel composed of a fused endosperm with two viable embryos. The two embryos were genetically distinct, indicating that they had arisen from independent fertilization events. These results suggest that cytokinin can determine pistil cell fate during maize floret development.

Abortion, Spontaneous↗

PubMed2004

ACC synthase expression regulates leaf performance and drought tolerance in maize.

Ethylene regulates entry into several types of plant developmental cell death and senescence programs besides mediating plant responses to biotic and abiotic stress. The response of cereals to conditions of drought includes loss of leaf function and premature onset of senescence in older leaves. In this study, ACC synthase (ACS) mutants, affecting the first step in ethylene biosynthesis, were isolated in maize and their effect on leaf function examined. Loss of ZmACS6 expression resulted in delayed leaf senescence under normal growth conditions and inhibited drought-induced senescence. Zmacs6 leaves continued to be photosynthetically active under both conditions indicating that leaf function was maintained. The delayed senescence phenotype associated with loss of ZmACS6 expression was complemented by exogenous ACC. Surprisingly, elevated levels of foliar chlorophyll, Rubisco, and soluble protein as well as improved leaf performance was observed for all Zmasc6 leaves, including young and fully expanded leaves which were far from initiating senescence. These observations suggest that ethylene may serve to regulate leaf performance throughout its lifespan as well as to determine the onset of natural senescence and mediate drought-induced senescence.

Chlorophyll↗

PubMed2003

Increasing vitamin C content of plants through enhanced ascorbate recycling.

Vitamin C (ascorbic acid) is essential to prevent disease associated with connective tissue (e.g., scurvy), improves cardiovascular and immune cell functions, and is used to regenerate alpha-tocopherol (vitamin E). In contrast to most animals, humans lack the ability to synthesize ascorbic acid as a result of a mutation in the last enzyme required for ascorbate biosynthesis. Vitamin C, therefore, must be obtained from dietary sources and, because it cannot be stored in the body, it must be obtained regularly. Once used, ascorbic acid can be regenerated from its oxidized form in a reaction catalyzed by dehydroascorbate reductase (DHAR). To examine whether overexpression of DHAR in plants would increase the level of ascorbic acid through improved ascorbate recycling, a DHAR cDNA from wheat was isolated and expressed in tobacco and maize, where DHAR expression was increased up to 32- and 100-fold, respectively. The increase in DHAR expression increased foliar and kernel ascorbic acid levels 2- to 4-fold and significantly increased the ascorbate redox state in both tobacco and maize. In addition, the level of glutathione, the reductant used by DHAR, also increased, as did its redox state. These results demonstrate that the vitamin C content of plants can be elevated by increasing expression of the enzyme responsible for recycling ascorbate.

Amino Acid Sequence↗