Laboratory of Fruit Quality Biology/The State Agriculture Ministry Laboratory of Horticultural Plant Growth, Development and Quality Improvement, Zhejiang University, Zijingang Campus, Hangzhou 310058, China.
J Exp Bot. 2012 Jan;63(1):341-54. doi: 10.1093/jxb/err284. Epub 2011 Oct 11.
Loquat (Eriobotrya japonica Lindl.) can be sorted into red- and white-fleshed cultivars. The flesh of Luoyangqing (LYQ, red-fleshed) appears red-orange because of a high content of carotenoids while the flesh of Baisha (BS, white-fleshed) appears ivory white due to a lack of carotenoid accumulation. The carotenoid content in the peel and flesh of LYQ was approximately 68 μg g(-1) and 13 μg g(-1) fresh weight (FW), respectively, and for BS 19 μg g(-1) and 0.27 μg g(-1) FW. The mRNA levels of 15 carotenogenesis-related genes were analysed during fruit development and ripening. After the breaker stage (S4), the mRNA levels of phytoene synthase 1 (PSY1) and chromoplast-specific lycopene β-cyclase (CYCB) were higher in the peel, and CYCB and β-carotene hydroxylase (BCH) mRNAs were higher in the flesh of LYQ, compared with BS. Plastid morphogenesis during fruit ripening was also studied. The ultrastructure of plastids in the peel of BS changed less than in LYQ during fruit development. Two different chromoplast shapes were observed in the cells of LYQ peel and flesh at the fully ripe stage. Carotenoids were incorporated in the globules in chromoplasts of LYQ and BS peel but were in a crystalline form in the chromoplasts of LYQ flesh. However, no chromoplast structure was found in the cells of fully ripe BS fruit flesh. The mRNA level of plastid lipid-associated protein (PAP) in the peel and flesh of LYQ was over five times higher than in BS peel and flesh. In conclusion, the lower carotenoid content in BS fruit was associated with the lower mRNA levels of PSY1, CYCB, and BCH; however, the failure to develop normal chromoplasts in BS flesh is the most convincing explanation for the lack of carotenoid accumulation. The expression of PAP was well correlated with chromoplast numbers and carotenoid accumulation, suggesting its possible role in chromoplast biogenesis or interconversion of loquat fruit.
枇杷（Eriobotrya japonica Lindl.）可分为红果肉和白果肉品种。洛阳青（LYQ，红果肉）的果肉因类胡萝卜素含量高而呈现橙红色，而白沙（BS，白果肉）的果肉因缺乏类胡萝卜素积累而呈现象牙白色。LYQ 的果皮和果肉中的类胡萝卜素含量分别约为 68μg g(-1)和 13μg g(-1)鲜重（FW），BS 分别为 19μg g(-1)和 0.27μg g(-1) FW。在果实发育和成熟过程中分析了 15 个与类胡萝卜素生物合成相关的基因的 mRNA 水平。在裂果期（S4）后，PSY1 和质体特异性番茄红素β-环化酶（CYCB）的 mRNA 水平在 LYQ 的果皮中较高，而 CYCB 和β-胡萝卜素羟化酶（BCH）的 mRNA 水平在 LYQ 的果肉中较高，与 BS 相比。还研究了果实成熟过程中的质体形态发生。BS 果皮中的质体超微结构在果实发育过程中的变化小于 LYQ。在 LYQ 果皮和果肉的完全成熟阶段观察到两种不同的质体形状。类胡萝卜素被包裹在 LYQ 和 BS 果皮的质体小球中，但在 LYQ 果肉的质体中呈结晶形式。然而，在完全成熟的 BS 果实果肉细胞中没有发现质体结构。LYQ 果皮和果肉中的质体脂质相关蛋白（PAP）的 mRNA 水平是 BS 果皮和果肉的五倍以上。总之，BS 果实中类胡萝卜素含量较低与 PSY1、CYCB 和 BCH 的 mRNA 水平较低有关；然而，BS 果肉中无法形成正常的质体是其缺乏类胡萝卜素积累的最令人信服的解释。PAP 的表达与质体数量和类胡萝卜素积累密切相关，表明其在质体生物发生或枇杷果实类胡萝卜素的相互转化中可能发挥作用。
