Cloning and Characterization of Genes Related to Betaine, the Effect of Salt on Cell Death and Competition on Atriplex Prostrata
Soil salinity is a major concern to agriculture all over the world because excess salts in the soil inhibit crop growth. Halophytes such as Atriplex prostrata are able to grow and reproduce in saline environments. One of the reasons A. prostrata is salt-tolerant is that it accumulates osmoprotectants such as glycine betaine in the cytosol and sequesters Na+ and Cl- into the vacuoles. In higher plants, glycine betaine is synthesized via the two-step oxidation of choline catalyzed by choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH). The cDNAs encoding CMO and BADH are cloned from A. prostrata (ApCMO and ApBADH1, respectively) by RT-PCR and 3-RACE. The composite cDNA, ApCMO, is 1669 bp long and encodes a full-length protein of 438 amino acids, with similar characteristics and a high degree of identity to other CMOs. The composite cDNA of A. prostrata BADH, designated as ApBADH1, is 1755 bp long and encodes a full-length protein of 500 amino acids. As in amaranth and in mangrove, Avicennia marina, there are two BADHs in A. prostrata. The second BADH, designated as ApBADH2, was discovered as a partial cDNA by RT-PCR. This ApBADH2 may be a peroxisomal BADH in A. prostrata. Both ApCMO and ApBADH1 expressions are salt-inducible and regulated in a developmental and organ-specific manner. However, ApCMO expression is ABA-independent while ApBADH1 expression may be ABA-dependent. The importance of glycine betaine was further demonstrated in a cell line of A. prostrata that does not express CMO. Approximately 70 % of these suspension-cultured cells die after being treated with 340 mM NaCl. NaCl also significantly reduces growth. Most of these cells are protected by exogenous addition of betaine indicated by reduced percentage of cell death and growth inhibition. In addition, NaCl-induced cell death in A. prostrata exhibits characteristics of programmed cell death. Since the growth of halophytes in a natural habitat is affected by both salinity and competition, the effects of i ntraspecific competition on growth and photosynthesis of A. prostrata are examined. The growth of A. prostrata from higher denisities is inhibited as a consequence of reduced photosynthesis due to competition for light.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:nacl choline monooxygenase betaine aldehyde dehydrogenase cell death glycine
Date of Publication:01/01/2002