Siboza Xolani Irvin, Bertling Isa, Odindo Alfred Oduor
Discipline of Horticultural Science, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, 3209 Pietermaritzburg, South Africa.
Discipline of Horticultural Science, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, 3209 Pietermaritzburg, South Africa.
J Plant Physiol. 2014 Nov 15;171(18):1722-31. doi: 10.1016/j.jplph.2014.05.012. Epub 2014 Aug 14.
Chilling injury (CI) is associated with the degradation of membrane integrity which can be aligned to phenolic oxidation activated by polyphenol oxidase (PPO) and peroxidase (POD), enzymes responsible for tissue browning. Phenylalanine ammonia-lyase (PAL) is a further enzyme prominent in the phenolic metabolism that is involved in acclimation against chilling stress. It was hypothesized that treatment with methyl jasmonate (MJ) and salicylic acid (SA) may enhance chilling tolerance in lemon fruit by increasing the synthesis of total phenolics and PAL by activating the key enzyme regulating the shikimic acid pathway whilst inhibiting the activity of POD and PPO. Lemon fruit were treated with 10μM MJ, 2mM SA or 10μM MJ plus 2mM SA, waxed, stored at -0.5, 2 or 4.5°C for up to 28 days plus 7 days at 23°C. Membrane integrity was studied by investigating membrane permeability and the degree of membrane lipid peroxidation in lemon flavedo following cold storage. The 10μM MJ plus 2mM SA treatment was most effective in enhancing chilling tolerance of lemon fruit, significantly reducing chilling-induced membrane permeability and membrane lipid peroxidation of lemon flavedo tissue. This treatment also increased total phenolics and PAL activity in such tissue while inhibiting POD activity, the latter possibly contributing to the delay of CI manifestation. PPO activity was found to be a poor biochemical marker of CI. Treatment with 10μM MJ plus 2mM SA resulted in an alteration of the phenolic metabolism, enhancing chilling tolerance, possibly through increased production of total phenolics and the activation of PAL and inhibition of POD.
冷害（CI）与膜完整性的降解有关，这可能与多酚氧化酶（PPO）和过氧化物酶（POD）激活的酚类氧化有关，这两种酶是导致组织褐变的原因。苯丙氨酸解氨酶（PAL）是酚类代谢中另一种重要的酶，参与对冷胁迫的适应。据推测，茉莉酸甲酯（MJ）和水杨酸（SA）处理可能通过激活调节莽草酸途径的关键酶来增加总酚和PAL的合成，同时抑制POD和PPO的活性，从而提高柠檬果实的耐冷性。柠檬果实分别用10μM MJ、2mM SA或10μM MJ加2mM SA处理，打蜡后，在-0.5、2或4.5°C下储存28天，再在23°C下储存7天。通过研究冷藏后柠檬外果皮的膜通透性和膜脂过氧化程度来研究膜完整性。10μM MJ加2mM SA处理在提高柠檬果实耐冷性方面最有效，显著降低了冷诱导的柠檬外果皮组织的膜通透性和膜脂过氧化。这种处理还增加了该组织中的总酚含量和PAL活性，同时抑制了POD活性，后者可能有助于延迟冷害症状的出现。发现PPO活性不是冷害的良好生化指标。10μM MJ加2mM SA处理导致酚类代谢发生改变，提高了耐冷性，可能是通过增加总酚的产生以及激活PAL和抑制POD来实现的。
