Molybdenum Efficiency Of Winter Wheat Genotypes And Its Physiological Bases

Based on the reviews of molybdenum nutrition and biosynthesis of chlorophyll, mechanism of molybdenum efficiency, its bases on absorption, transportation and distribution of molybdenum and nitrogen, on biochemistry and physiology, as well as the effect of molybdenum on the biosynthesis of chlorophyll of winter wheat cultivars were conducted in acid brown yellow earth with low available molybdenum. The results were as the following. 1.One Mo high efficiency winter wheat genotype(97003) and one Mo low efficiency winter wheat genotype(97014), with MoER beyond 0.95 and below 0.6, were obtained by the screening method using Mo efficiency ratio (MoER), ratio of grain yields between Mo insufficient treatment(CK) and Mo sufficient treatment(+Mo) (CK/+Mo) in two years' successive experiments.2.Cultivar 97003 had the capacity of uptake more Mo (N) from low Mo soil, could transport and/or retranslocate more Mo(N) from the stem to the spikes and the seed.3.Mo deficiency led to abnormal nitrogen nutrition of winter wheat cultivars. The plant absorbed and made use of less nitrogen while the totle nitrogen content was much higher in plant of Mo insufficient treatment than that of Mo sufficient treatment, which could not be explained clearly by dilution effect However, nitrogen nutrition of cultivar 97003 was less disturbed than cultivar 97014,4.Cultivar 97003 had the high systems of nitrate reductase(NR) and glutamine synthetase(GS), especially in short of Mo which counted. GS isoenzyme analysis by gradient elution showed that the difference in GS activity was from GS₂, the GS in the chloroplast which was mainly involved in assimilation of the ammonium released from photorespiration. Mo deficiency also led to high activity of GS which suggested the direct use of ammonium, also the increase of photorespiration if the increase of asparagine synthetase(AS) and ammonium, the extra-accumulation of serine and significant drop of glycine were also added. So, it seemed that photorespiration could be lowered by Mo application. 5 Free amino acids, soluble protein, chlorophyll, catalase, carotenoids were higher in 97003 than that of 97014 especially in short of molybdenum, which means metabolism of 97003 was less disturbed by molybdenum deficiency and these above were the bases of molybdenum high efficiency.6.Glutamate, the precusor of ALA (5-aminolevulinic acid) synthesis in higher plants, accumulated in large qualities in leaf blade of Mo deficiency plant showed that the transformation of glutamate was inhibited. ALA was the common precursor of tetrapyrole ring. The decrease in the content of chlorophyll, also activity of catalase and peroxidase in the treatment indicated the biosynthesis of tetrapyrole ring was repressed by Mo deficiency.7.Mo deficiency led to variations of the amount of precusors in chlorophyll biosynthesis. The results that ProtoIX, Mg-ProtoK and protochlorophyll decreased in a assimiliar way, Uroâ…¢ decreased and ALA increased significantly when Mo was deficient showed the transformation of ALA to Uroâ…¢ was suppressed by Mo shortage. While treated with LA, the suppressor of ALA transformation, plant in Mo deficiency did not accumulated any more ALA than that of Mo sufficiency, on the contrary, Content of ALA in plant of Mo deficiency was significantly lower than that of Mo sufficiency, which indicated that the formation of ALA was also inhibited. Thus, chlorophyll biosynthesis was inhibited in ALA formation and transformation by Mo deficiency.8.The structure of chloroplast was also disturbed by Mo deficiency, especially in the molybdenum low efficiency genotype. The size, number of chloroplast decreased, chloroplasts was separated to single chloroplast. Chloroplast and mitochondria! turned into circular shape from streamlike shape, grana lamellae developed poorly and the number of grana lamellae was less.From the results above, Mo nutritional mechanism was inferred to involve the inhibition of carbon metabolism besides the inhibition of nitrogen.