Shivashankar Seshadri, Sumathi Manoharan
Division of Plant Physiology and Biochemistry, Indian Institute of Horticultural Research, Bangalore, India,
J Biosci. 2015 Jun;40(2):375-87. doi: 10.1007/s12038-015-9515-7.
Spongy tissue is a physiological disorder in Alphonso mango caused by the inception of germination-associated events during fruit maturation on the tree, rendering the fruit inedible. Inter-fruit competition during active fruit growth is a major contributing factor for the disorder which leads to reduced fat content in spongy tissue affected fruits. This study was, therefore, carried out to determine the possible association between seed fats and ST formation. The study of the fat content during fruit growth showed that it increased gradually from 40 percent fruit maturity. At 70 percent maturity, however, there was a sudden increase of fat content of whole fruit, leading to acute competition and resulting in differential allocation of resources among developing fruits. As a result, the seed in spongy-tissue-affected mature ripe fruit showed a marked drop in the levels of fats and the two very long chain fatty acids (VLCFAs), tetracosanoic acid and hexacosanoic acid together with an increase of linolenic acid and a fall in oleic acid contents, which are known to be key determinants for the initiation of pre-germination events in seed. Subsequently, a rise in the level of cytokinin and gibberellins in ST seed associated with a fall in abscisic acid level clearly signalled the onset of germination. Concurrently, a significant reduction in the ratio of linolenic acid/linoleic acid in pulp led to the loss of membrane integrity, cell death and the eventual formation of spongy tissue. Based on the above, it is concluded that a significant reduction in the biosynthesis of VLCFAs in seeds during fruit growth might trigger pre-germination events followed by a cascade of biochemical changes in the pulp, leading to lipid peroxidation and membrane injury in pulp culminating in ST development. Thus, this study presents crucial experimental evidence to highlight the critical role played by VLCFAs in inducing ST formation in Alphonso mango during the pre-harvest phase of fruit growth.
海绵组织是阿方索芒果的一种生理病害，由果实挂在树上成熟期间与萌发相关的事件引发，导致果实无法食用。果实快速生长期间的果实间竞争是该病害的一个主要促成因素，这会导致受海绵组织影响的果实脂肪含量降低。因此，本研究旨在确定种子脂肪与海绵组织形成之间可能存在的关联。对果实生长期间脂肪含量的研究表明，从果实成熟度达到40%起，脂肪含量逐渐增加。然而，在成熟度达到70%时，整个果实的脂肪含量突然增加，导致激烈竞争，进而造成发育中的果实之间资源分配不均。结果，受海绵组织影响的成熟果实中的种子脂肪水平显著下降，两种极长链脂肪酸（VLCFAs）——二十四烷酸和二十六烷酸的含量也下降，同时亚麻酸含量增加，油酸含量下降，而这些已知是种子萌发前事件启动的关键决定因素。随后，海绵组织种子中细胞分裂素和赤霉素水平升高，同时脱落酸水平下降，这清楚地表明萌发开始。与此同时，果肉中亚麻酸/亚油酸比例显著降低，导致膜完整性丧失、细胞死亡，最终形成海绵组织。基于上述情况，得出的结论是，果实生长期间种子中极长链脂肪酸生物合成的显著减少可能会引发萌发前事件，随后果肉中发生一系列生化变化，导致果肉中的脂质过氧化和膜损伤，最终导致海绵组织的形成。因此，本研究提供了关键的实验证据，以突出极长链脂肪酸在果实生长收获前阶段诱导阿方索芒果海绵组织形成中所起的关键作用。
