Mitochondrial alterations during Al-induced PCD in peanut root tips.

Previous study found there was a negative relationship between Al-induced PCD and Al-resistance in peanut. The present research was undertaken to verify whether mitochondria play a significant role in PCD induced by Al in peanut. The roots of Al-tolerant plants were found to exhibit more intensive root growth, while accumulating less Al³âº than Al-sensitive plants under Al treatment. The different enhancement of ROS production was observed in the mitochondria isolated from two peanut cultivars. The concentration of mitochondrial MDA in root tips increased after Al treatment, which was higher in Zhonghua 2 than in 99-1507. With the increase of Al concentration, mitochondrial Ca²âº concentration decreased, and Ca²âº concentration of Zhonghua 2 decreased faster than that of 99-1507. The opening of mitochondrial permeability transition pore was more extensively in mitochondria isolated from Zhonghua 2 than from 99-1507. The collapse of inner mitochondrial membrane potential (ΔΨm) was also observed with a release of Cytochrome c (Cyt c) from mitochondria, it was more obvious in Zhonghua 2 than in 99-1507 with Al concentration increasing. The results showed that mitochondrial membrane structure and function were damaged seriously in Al-induced PCD, the increase of mitochondrial antioxidant system activity decreased cellular damages under Al stress. To sum up, compared with Al-sensitive peanut cultivar, Al-tolerant peanut cultivar has less Al³âº absorption, mitochondrial ROS and membrane lipid peroxidation level, higher control of MPT opening, ΔΨm maintaining, Cty c release from mitochondria and mitochondrial respiratory functions so that it is not easy to produce PCD under Al stress.

Aluminum induces rapidly mitochondria-dependent programmed cell death in Al-sensitive peanut root tips.

BACKGROUND: Although many studies suggested that aluminum (Al) induced programmed cell death (PCD) in plants, the mechanism of Al-induced PCD and its effects in Al tolerance is limited. This study was to investigate the mechanism and type of Al induced PCD and the relationship between PCD and Al tolerance. RESULTS: In this study, two genotypes of peanut 99-1507 (Al tolerant) and ZH2 (Al sensitive) were used to investigate Al-induced PCD. Peanut root growth inhibition induced by AlCl3 was concentration and time-dependent in two peanut varieties. AlCl3 at 100 µM could induce rapidly peanut root tip PCD involved in DNA cleavage, typical apoptotic chromatin condensation staining with DAPI, apoptosis related gene Hrs203j expression and cytochrome C (Cyt c) release from mitochondria to cytosol. Caspase3-like protease was activated by Al; it was higher in ZH2 than in 99-1507. Al increased the opening of mitochondrial permeability transition pore (MPTP), decreased inner membrane potential (ΔΨm) of mitochondria. Compared with the control, Al stress increased O2•- and H2O2 production in mitochondria. Reactive oxygen species (ROS) burst was produced at Al treatment for 4 h. CONCLUSIONS: Al-induced PCD is earlier and faster in Al-sensitive peanut cultivar than in Al-tolerant cultivar. There is a negative relationship between PCD and Al resistance. Mitochondria- dependence PCD was induced by Al and ROS was involved in this process. The mechanism can be explained by the model of acceleration of senescence under Al stress.

Aluminum-induced programmed cell death promoted by AhSAG, a senescence-associated gene in Arachis hypoganea L.

Programmed cell death (PCD) is a foundational cellular process in plant development and elimination of damaged cells under environmental stresses. In this study, Al induced PCD in two peanut (Arachis hypoganea L.) cultivars Zhonghua 2 (Al-sensitive) and 99-1507 (Al-tolerant) using DNA ladder, TUNEL detection and electron microscopy. The concentration of Al-induced PCD was lower in Zhonghua 2 than in 99-1507. AhSAG, a senescence-associated gene was isolated from cDNA library of Al-stressed peanut with PCD. Open reading frame (ORF) of AhSAG was 474bp, encoding a SAG protein composed of 157 amino acids. Compared to the control and the antisense transgenic tobacco plants, the fast development and blossom of the sense transgenic plants happened to promote senescence. The ability of Al tolerance in sense transgenic tobacco was lower than in antisense transgenic tobacco according to root elongation and Al content analysis. The expression of AhSAG-GFP was higher in sense transgenic tobacco than in antisense transgenic tobacco. Altogether, these results indicated that there was a negative relationship between Al-induced PCD and Al-resistance in peanut, and the AhSAG could induce or promote the occurrence of PCD in plants.

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.

[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.