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Starch content and activities of some enzymes of starch metabolism were determined in wild-type, N2-fixing (fix+) nodules and in two non-N2-fixing (fix−) nodules induced by Bradyrhizobium japonicum mutant strains, T5-95 and T8-1, on soybean (Glycine max L.) roots. The T5-95 nodules are similar to wild type in ultrastructure, but the T8-1 nodules are different in that the bacteroids are not released from the infection thread. After initial accumulation to relatively high concentration, starch was depleted during nitrogen fixation in fix+ nodules. However, in fix− nodules, the accumulated starch was not metabolized. The activity of starch-bound starch synthase (EC 2.4.1.21) declined in fix+ nodules but remained high in fix− nodules. The activity of α-amylase (EC 3.2.1.1) was only slightly higher than wild type in T5-95 but was four times higher than wild type in T8-1 nodules. The activity of starch phosphorylase (EC 2.4.1.1) increased in all nodule types from 14 to 21 days postinfection. A positive correlation was observed between the capacity of nodules to fix N2 and their capacity to degrade starch. Collectively, these results support the concept that starch accumulated during early stages of nodule development is metabolized to supply energy for nitrogen fixation and to meet the metabolic demands of bacteroids. Key words: nitrogen fixation, starch content, effective and ineffective nodules, starch synthase, starch phosphorylase, α-amylase.

Boron-phosphorus interaction was observed in maize (Zea mays L. ’Ganga 2’) when grown in refined sand at three levels of boron, deficient (0.0033 mg L−1), normal (0.33 mg L−1) and excess (3.3 mg L−1), each at three levels of phosphorus, deficient (0.17 m mol L−1), normal (1.5 mmol L−1) and excess (4 m mol L−1). The effects of phosphorus deficiency (i.e., reduction in dry matter, soluble protein, DNA, activity of ribonuclease and increase in the activities of peroxidase, acid phosphatase and polyphenol oxidase) were intensified by a combined deficiency of boron and phosphorus. The effects of boron deficiency (i.e., reduction in dry weight, leaf boron and DNA and increase in starch content and in the activities of starch phosphorylase, peroxidase and polyphenol oxidase) become more intense in the treatment-deficient B-excess P. The decreases caused by excess phosphorus (i.e., dry weight, starch and sugar content, DNA, RNA and activity of ribonuclease) were aggravated by combined excess of boron and phosphorus.Key words: Zea mays, maize, boron and phosphorus nutrition

A reduction in the size of tassels, male flowers, and anthers resulted from molybdenum deficiency in maize. In molybdenum-deficient plants, anthesis was suppressed or delayed and the anthers had fewer and smaller pollen grains that lacked dense cytoplasmic contents, appeared shrivelled, and had poor viability. Because of molybdenum deficiency, there was a decrease in the activity of starch phosphorylase in mature and freshly shed pollen grains and decreases in the activities of invertase and acid phosphatase at all the five stages at which pollen grains were assayed for the enzymes. The activities of catalase and peroxidase were increased by molybdenum deficiency at all five stages and that of ribonuclease at four out of the five stages of pollen development.