Effect of shading on zinc deficiency symptoms in rice plant

Abstract

933Under Zn deficiency, some major deficiency symptoms were observed on rice plants, i.e., reduction of young leaf elongation and development of necrosis on the expanded leaves. To clarify the former phenomena, the physiological role of Zn was studied from the standpoint of protein synthesis (Kitagishi and Obata 1986;Obata et al. 1994Obata et al. , 1996 and metabolism of auxin (Takaki and Arita 1986;Domingo et al. 1992). In contrast, the direct cause of the latter phenomenon has not yet been studied. Vaughan et al. (1982) showed that the superoxide dismutase (SOD) activity was depressed under Zn deficiency in fronds of Lemna gibba. Cakmak and Marshner (1988) revealed that under Zn deficiency, the activities of SOD and catalase were depressed in cotton, beans, and tomatoes and the deficient plants accumulated superoxide radical (0 2 -) in their roots. O 2 -is known to cause severe peroxidative damage to various cellular components, i.e., membrane fatty acids, proteins, and chlorophyll (Elstner 1982). Based on these data, it is assumed that O 2 -accumulated under Zn deficiency may induce deficiency symptoms in rice plants. Kitagishi and Obata (1986) revealed that the concentration of protein decreased and that of free amides and amino acids increased by Zn deficiency in the meristem tissues of rice plant. In this paper, as the first step to analyze the effect of Zn deficiency from the standpoint of photo-oxidation, the effect of shading on clinical symptoms and protein concentration in the meristem tissues of rice plants under Zn deficiency was determined. Materials and methodsRice plants, Oryza sativa L. cv. Koshihikari were germinated on a plastic net. After 14 d, on May 30, the plants were transferred to styrene foam square holders and cultured in a glass house under natural light conditions with a Kimura B solution for rice culture supplemented with Fe 5 as Fe 2 0 3 , Mn 0.25, Cu 0.01, B 0.2, and Mo 0.01 mg L -1 with (+ Zn) and without (~Zn) the addition of Zn 0.025 mg L -1. The initial pH was 5.4 and each solution was renewed once a week. Immediately after the zinc deficiency symptoms, consisting of a reduction of plant height, were observed in the ~Zn plot, on June 15, some pots with and without Zn were shaded using a double layer of cheese cloth to decrease the sunlight intensity to 65% of the full strength.Rice shoots were harvested 7 d after shading and were separated into leaf blades and leaf sheaths that enclosed all the younger parts of the shoot. The emerging leaf was sampled after stripping the leaf sheaths manually and 10 mm pieces from the base of the emerging leaf were

Tansley Review No. 111

“…3c). Similar results have also been shown for citrus (Cakmak et al, 1995) and rice plants (Obata et al, 1997). In citrus orchards in California, Zn deficiency chlorosis has been reported to be more severe on branches directly exposed to sunlight (Chapman, 1966).…”

Changes in the level of protein and activity of Cu/Zn-superoxide dismutase in zinc deficient rice plant,Oryza sativaL.

“…The mechanism of occurrence of the deficiency symptoms has not been fully elucidated. The authors (Obata et al 1997) showed that the necrosis was alleviated by shading. The results suggest that the symptoms may be caused by a failure of O 2 -scavenging and elevation of O 2 -level due to Cu/Zn superoxide dismutase (Cu/Zn-SOD) shortage.…”