The Level of Expression of Thioredoxin is Linked to Fundamental Properties and Applications of Wheat Seeds

Work with cereals （barley and wheat） and a legume （Medicago truncatula） has established thioredoxin h （Trx h） as a central regulatory protein of seeds. Trx h acts by reducing disulfide （S-S） groups of diverse seed proteins （storage proteins, enzymes, and enzyme inhibitors）, thereby facilitating germination. Early in vitro protein studies were complemented with experiments in which barley seeds with Trx h overexpressed in the endosperm showed accelerated germination and early or enhanced expression of associated enzymes （α-amylase and pullulanase）. The current study extends the transgenic work to wheat. Two approaches were followed to alter the expression of Trx h genes in the endosperm： （1） a hordein promoter and its protein body targeting sequence led to overexpression of Trx hS, and （2） an antisense construct of Trx h9 resulted in cytosolic underexpression of that gene （Arabidopsis designation）. Underexpression of Trx h9 led to effects opposite to those observed for overexpression Trx h5 in barley--retardation of germination and delayed or reduced expression of associated enzymes. Similar enzyme changes were observed in developing seeds. The wheat lines with underexpressed Trx showed delayed preharvest sprouting when grown in the greenhouse or field without a decrease in final yield. Wheat with overexpressed Trx h5 showed changes commensurate with earlier in vitro work： increased solubility of disulfide proteins and lower aUergenicity of the gliadin fraction. The results are further evidence that the level of Trx h in cereal endosperm determines fundamental properties as well as potential applications of the seed.

Transgenic barley with overexpressed PTrx increases aluminum resistance in roots during germination

A transgenic barley line(LSY-11-1-1) with overexpressed Phalaris coerulescens thioredoxin gene(PTrx) was employed to measure the growth,protein oxidation,cell viability,and antioxidase activity in barley roots during germination on the presence of 2 mmol/L AlCl3 on filter paper.The results show that(1) compared with the non-transgenic barley,LSY-11-1-1 had enhanced root growth,although both were seriously inhibited after AlCl3 treatment;(2) the degree of protein oxidation and loss of cell viability in roots of LSY-11-1-1 were much less than those in roots of non-transgenic barley,as reflected by lower contents of protein carbonyl and Evans blue uptakes in LSY-11-1-1;(3) activities of catalase(CAT) ,glutathione peroxidase(GPX) ,ascorbate peroxidase(APX) ,and glu-tathione reductase(GR) in LSY-11-1-1 root tips were generally higher than those in non-transgenic barley root tips,although these antioxidase activities gave a rise to different degrees in both LSY-11-1-1 and non-transgenic barley under aluminum stress.These results indicate that overexpressing PTrx could efficiently protect barley roots from oxidative injury by increasing antioxidase activity,thereby quenching ROS caused by AlCl3 during germination.These properties raise the possibility that transgenic barley with overexpressed PTrx may be used to reduce the aluminum toxicity in acid soils.