Manganese Toxicity in Sugarcane Plantlets Grown on Acidic Soils of Southern China.

Ratoon sugarcane plantlets in southern China have suffered a serious chlorosis problem in recent years. To reveal the causes of chlorosis, plant nutrition in chlorotic sugarcane plantlets and the role of manganese (Mn) in this condition were investigated. The study results showed that the pH of soils growing chlorotic plantlets ranged from 3.74 to 4.84. The symptoms of chlorosis were similar to those of iron (Fe) deficiency while the chlorotic and non-chlorotic plantlets contained similar amount of Fe. Chlorotic plantlets had 6.4-times more Mn in their leaf tissues compared to the control plants. There was a significantly positive correlation between Mn concentration in the leaves and the exchangeable Mn concentration in the soils. Moreover, leaf Mn concentration was related to both seasonal changes in leaf chlorophyll concentration and to the occurrence of chlorosis. Basal stalks of mature sugarcanes contained up to 564.36 mg·kg(-1) DW Mn. Excess Mn in the parent stalks resulted in a depress of chlorophyll concentration in the leaves of sugarcanes as indicated by lower chlorophyll concentration in the leaves of plantlets emerged from basal stalks. Ratoon sugarcane plantlets were susceptible to chlorosis due to high Mn accumulation in their leaves (456.90-1626.95 mg·kg(-1) DW), while in planted canes chlorosis did not occur because of low Mn accumulation (94.64-313.41mg·kg(-1) DW). On the other hand, active Fe content in chlorotic plantlets (3.39 mg kg(-1) FW) was only equivalent to 28.2% of the concentration found in the control. These results indicate that chlorosis in ratoon sugarcane plantlets results from excessive Mn accumulated in parent stalks of planted cane sugarcanes grown on excessive Mn acidic soils, while active Fe deficiency in plantlets may play a secondary role in the chlorosis.

Nitric oxide improves aluminum tolerance by regulating hormonal equilibrium in the root apices of rye and wheat.

Nitric oxide (NO) has emerged as a key molecule involved in many physiological processes in plants. Whether NO reduces aluminum (Al) toxicity by regulating the levels of endogenous hormones in plants is still unknown. In this study, the effects of NO on Al tolerance and hormonal changes in the root apices of rye and wheat were investigated. Rye was more tolerant to Al stress than wheat according to the results of root elongation and Al content determined. Root inhibition exposed to Al was in relation to Al accumulation in the root apices. Al treatment decreased GA content and increased the values of IAA/GA and ABA/GA. Supplementation of NO donor sodium nitroprusside (SNP) reduced the inhibition of root elongation by increasing GA content and decreasing the values of IAA/GA and IAA/ZR under Al stress. NO scavenger 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylinidazoline-1-oxyl-3-oxide (cPTIO) can reversed SNP alleviating effect on Al toxicity. However, the regulating patterns of NO on the values of ABA/GA, GA/ZR and ABA/(IAA+GA+ZR) were different between rye and wheat. The values of ABA/GA and ABA/(IAA+GA+ZR) increased in rye, but decreased in wheat. The change of GA/ZR value was opposite. These results suggest that NO may reduce Al accumulation in the root apices by regulating hormonal equilibrium to enhance Al-tolerance in plants, which effect is more remarkable in Al-sensitive wheat.

[Characteristics of N forms and N-transforming bacteria in paddy soil under different tillage patterns].

Paddy soil samples were collected in layers (0-5, 5-12, and 12-20 cm) during rice growth period to investigate the characteristics of the N forms and N-transforming bacteria in the soil profile under different tillage patterns (no-tillage with straw returning, NTS; conventional tillage with straw returning, CTS; no-tillage, NT; and conventional tillage, CT). In the whole rice growth period, ammonifying bacteria in 0-5 cm soil layer had the highest number under NTS, and nitrosobacteria in 0-5 cm and 5-12 cm soil layers were more abundant but in 12-20 cm soil layer were lesser under CT than under NT. Nitrosobacteria and denitrobacteria in 0-20 cm soil layer were lesser under NTS than under CTS. At elongating and ripening stages, anaerobic N-fixing bacteria in 0-5 cm soil layer were more abundant under NT than under CT. In the whole rice growth period, the alkali-hydrolyzable N and total N contents in 0-5 cm soil layer were significantly higher but in 5-12 cm and 12-20 cm soil layers were lower under NT than under CT, and the NH4(+)-N and NO3(-)-N contents in 0-20 cm soil layer were higher under NTS but in 12-20 cm soil layer had no significant differences between NT and CT. Correlation analysis and multiple polynomial regression analysis further revealed that there were significant relationships between soil NH4(+)-N and soil ammonifying bacteria, nitrosobacteria and denitrobacteria, and between soil alkali-hydrolyzable N and soil anaerobic N-fixing bacteria. Among the test tillage patterns, NTS could be the more desirable one for the N supply and fertility maintenance of paddy soil.

[Effects of sodium nitroprusside on mitochondrial function of rye and wheat root tip under aluminum stress].

Sodium nitroprusside (SNP) could ameliorate the inhibition effect of Al on root growth of rye (Secale cereale L. cv. King) and wheat (Triticum aestivum L. cv. Jinmai47). Respiratory rate, P/O, OPR (oxygenated phosphate rate), R(3) (oxygen consumption rate with ADP and substrate present), R(4) (oxygen consumption rate with substrate) and RCR (respiratory control ratio, R(3)/R(4)) of root tips from rye and wheat decreased, as well as the activities of H(+)-ATPase, H(+)-PPase, Na(+)-K(+)-ATPase, Ca(2+)-ATPase and Mg(2+)-ATPase, but they increased with SNP treatment. It showed that mitochondrial respiratory functions of root tips from rye and wheat were damaged, phosphorylation was un-coupled by Al, but that of rye was less than that of wheat. Rye has high Al-resistance ability than wheat. SNP is one of donor of NO, it is suggested that NO can ameliorate remarkably respiratory dysfunction resulted from Al stress, so that NO can ameliorate the inhibition effect of Al on plant growth.