Zou Ying-Ning, Wu Qiang-Sheng, Huang Yong-Ming, Ni Qiu-Dan, He Xin-Hua
College of Horticulture and Gardening, Yangtze University, Jingzhou, China.
PLoS One. 2013 Nov 18;8(11):e80568. doi: 10.1371/journal.pone.0080568. eCollection 2013.
Proline accumulation was often correlated with drought tolerance of plants infected by arbuscular mycorrhizal fungi (AMF), whereas lower proline in some AM plants including citrus was also found under drought stress and the relevant mechanisms have not been fully elaborated. In this study proline accumulation and activity of key enzymes relative to proline biosynthesis (▵(1)-pyrroline-5-carboxylate synthetase, P5CS; ornithine-δ-aminotransferase, OAT) and degradation (proline dehydrogenase, ProDH) were determined in trifoliate orange (Poncirus trifoliata, a widely used citrus rootstock) inoculated with or without Funneliformis mosseae and under well-watered (WW) or water deficit (WD). AMF colonization significantly increased plant height, stem diameter, leaf number, root volume, biomass production of both leaves and roots and leaf relative water content, irrespectively of water status. Water deficit induced more tissue proline accumulation, in company with an increase of P5CS activity, but a decrease of OAT and ProDH activity, no matter whether under AM or no-AM. Compared with no-AM treatment, AM treatment resulted in lower proline concentration and content in leaf, root, and total plant under both WW and WD. The AMF colonization significantly decreased the activity of both P5CS and OAT in leaf, root, and total plant under WW and WD, except for an insignificant difference of root OAT under WD. The AMF inoculation also generally increased tissue ProDH activity under WW and WD. Plant proline content significantly positively correlated with plant P5CS activity, negatively with plant ProDH activity, but not with plant OAT activity. These results suggest that AM plants may suffer less from WD, thereby inducing lower proline accumulation, which derives from the integration of an inhibition of proline synthesis with an enhancement of proline degradation.
脯氨酸积累通常与丛枝菌根真菌（AMF）感染的植物的耐旱性相关，然而在一些包括柑橘在内的AM植物中，干旱胁迫下也发现脯氨酸含量较低，且相关机制尚未完全阐明。在本研究中，测定了接种或未接种摩西管柄囊霉的枳（一种广泛使用的柑橘砧木）在充分供水（WW）或水分亏缺（WD）条件下脯氨酸的积累以及与脯氨酸生物合成（△¹-吡咯啉-5-羧酸合成酶，P5CS；鸟氨酸-δ-转氨酶，OAT）和降解（脯氨酸脱氢酶，ProDH）相关的关键酶的活性。无论水分状况如何，AMF定殖均显著增加了植株高度、茎粗、叶片数量、根体积、叶和根的生物量以及叶片相对含水量。水分亏缺诱导更多组织脯氨酸积累，同时P5CS活性增加，但OAT和ProDH活性降低，无论是否接种AMF。与未接种AMF处理相比，在WW和WD条件下，接种AMF处理的叶片、根和全株中的脯氨酸浓度和含量均较低。在WW和WD条件下，AMF定殖显著降低了叶片、根和全株中P5CS和OAT的活性，但WD条件下根OAT的差异不显著。接种AMF通常也增加了WW和WD条件下组织ProDH的活性。植物脯氨酸含量与植物P5CS活性显著正相关，与植物ProDH活性负相关，但与植物OAT活性无关。这些结果表明，AM植物可能受水分亏缺的影响较小，从而诱导较低的脯氨酸积累，这源于脯氨酸合成抑制和脯氨酸降解增强的综合作用。
