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Da Man, Yong-Xia Bao, Lie-Bao Han, and Xunzhong Zhang

biochemical responses to drought stress. Accumulation of osmotic compounds such as proline and changes in phytohormones are some of the most common responses of plants to drought stress ( Hare et al., 1997 ). Proline, an amino acid, is a compatible solute

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Camilo Escalante-Magaña, Luis F. Aguilar-Caamal, Ileana Echevarría-Machado, Fátima Medina-Lara, Lucila Sánchez Cach, and Manuel Martínez-Estévez

inside the cell in high concentrations without causing metabolic harm such as polyols, which include sorbitol, mannitol, arabitol, and glycerol, and amino acids, which include proline (Pro), the quaternary amine glycine betaine (GB

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Huai-Fu Fan, Chang-Xia Du, and Shi-Rong Guo

are more important than inorganic ions for plants when they suffer environmental stresses. Proline, glycine betaine, and soluble sugars are examples of low-molecular-weight solutes that accumulate in plants. Pro is one of the most commonly accumulated

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Dipayan Sarkar, Prasanta C. Bhowmik, Young-In-Kwon, and Kalidas Shetty

phenylpropanoid pathway and the production of proline in plants during abiotic stress is well documented ( Christie et al., 1994 ; Dorffling et al., 1997 ). Studies in wheat indicated higher accumulation of proline during acclimation and its association in

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Kurt D. Nolte, Andrew D. Hanson, and Douglas A. Gage

Proline and various betaines can function as osmoprotectants and cryoprotectants when accumulated in the cytoplasm of cells. Genetic engineering can raise levels of these compounds and thereby improve stress resistance; Citrus species are potential candidates for this. Before attempting such engineering, it is necessary to characterize the natural osmoprotectants of Citrus and related genera. We therefore surveyed 55 cultivated and wild species of the Aurantioideae, analyzing proline and betaines in leaves of mature trees. Some citrus relatives accumulated proline alone; others accumulated proline and proline betaine, as did all Citrus species studied. The levels of these two compounds ranged from about 20 to 100 μmol·g-1 dry mass, and were significantly inversely correlated. Proline betaine is known to be synthesized from proline and to be a better osmoprotectant. Because Citrus species all have more proline than proline betaine, there is scope for engineering more of the latter. Many species had small amounts of hydroxyproline betaine; other betaines were essentially absent. The lack of other betaines means that it would also be rational to engineer the accumulation of glycine betaine or similar compounds.

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Cong Li, Lie-Bao Han, and Xunzhong Zhang

adjustment in response to drought ( Takahara and Akashi, 2006 ). Proline, one of the important compatible solutes, plays an important role in adjusting cell osmotic potential, maintaining plasma membrane integrity, and acting as a signaling molecule in

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G.C. Munshaw, X. Zhang, and E.H. Ervin

wish to thank J. Syvertsen and Y. Levy for their assistance with proline determination.

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Xinhua Zhang, Fujun Li, Nana Ji, Shujun Shao, Dongyang Wang, Ling Li, and Fansheng Cheng

; Jubault et al., 2008 ). Arginase hydrolyzes arginine to urea and ornithine, the latter of which contributes to the biosynthesis of both polyamines and proline ( Jubault et al., 2008 ). Research on the role of arginase in stress responses in plants has

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Alefsi David Sánchez-Reinoso, Gustavo Adolfo Ligarreto-Moreno, and Hermann Restrepo-Díaz

; Mohamed and Ibrahim, 2011 ). In this sense, it has been reported that susceptible genotypes accumulate less dry matter and produce different proline concentrations, which means that those genotypes have a better osmotic adjustment ( Sánchez-Rodríguez et al

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Zhanguo Xin and Paul H. Li

Exogenous proline and ABA can induce chilling tolerance. Whether there is any relationship between the proline and ABA in inducing chilling tolerance is not known. We attempted to elucidate their interrelationship by comparing the time course of proline and ABA induced chilling tolerance and of the uptake of proline and ABA in the cultured cells of maize (Zea mays L. Black Mexican Sweet). The uptake of proline was increasing continually during a 24 h culture at 28°C. However, the proline induced chilling tolerance became significant after 6 h treatment and reached maximum after 12 h. When cells were transferred to a ABA-containing medium the uptake of ABA in the cells reached almost plateau in 2 h period. The ABA induced chilling tolerance was insignificant at 6 h, became significant at 12 h, and reached maximum at 24 h. Although the rate of ABA induced chilling tolerance was slower than the rate of proline induced chilling tolerance, there was no any increase in endogenous free proline in the ABA treated cells. Statistical analysis indicates that there is no interrelationship between proline and ABA in the induction of chilling tolerance in maize. ABA induces specific proteins which may play essential role(s) in the development of chilling tolerance. None of these proteins was observed in proline treated cells. We concluded that the induction mechanisms of chilling tolerance between proline and ABA are independent in maize.