Effects of bicarbonate and high pH on growth of Zn-efficient and Zn-inefficient genotypes of rice, wheat and rye

A range of Zn efficient and inefficient genotypes of rice (Oryza sativa L.), wheat (Triticum aestivum L. and Triticum durum L.) and rye (Secale cereale L.) were investigated to examine shoot and root growth response to bicarbonate and high pH at different Zn levels. The treatment of bicarbonate was 10 mM as NaHCO3, high pH was 8.0 buffered with HEPES, and three Zn levels included without addition of Zn (deficient Zn), with 0.5 and 1.0 muM Zn (moderate Zn), and 1.5 and 3.5 muM (high Zn) for rice and wheat or rye, respectively. For rice, shoot and root growth of Zn-inefficient genotypes was strongly inhibited, whereas root length of Zn-efficient genotypes was considerably enhanced by bicarbonate. High pH had much less effect on reduced root growth of the Zn-inefficient rice genotypes and enhanced root length of the Zn-efficient genotypes, as compared with bicarbonate. Responses of plants to bicarbonate at different Zn levels showed that under deficient or moderate Zn supply conditions, root dry weight and length were significantly increased for the Zn-efficient rice genotypes, but were decreased for the Zn-inefficient rice genotypes grown with bicarbonate. At high Zn supply, however, root elongation of the Zn-efficient rice genotypes and of the Zn-inefficient genotypes was enhanced. In contrast to rice, either bicarbonate or high pH had little effects on shoot and root growth for all the Zn-efficient and Zn-inefficient wheat genotypes except for Dagdas (Zn-efficient) at moderate Zn levels. Decreased root growth due to bicarbonate treatment was observed only in the Zn-efficient rye. Root lengths of all the wheat and rye genotypes except for Kunduru (Zn-inefficient) were reduced by high pH but not affected by bicarbonate. At deficient Zn levels, shoot growth was reduced by bicarbonate for both Zn-efficient rye and inefficient wheat genotypes. Root lengths was reduced due to bicarbonate for the Zn-inefficient wheat genotype at deficient and high Zn, but not at moderate Zn levels. The results imply that Zn efficiency in rice is closely associated with plant tolerance to bicarbonate relative to root growth, and bicarbonate tolerance and Zn efficiency might be developed simultaneously in lowland rice.