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Sacred lotus (Nelumbo nucifera) is an important aquatic ornamental plant which contains several diverse flower colors, but the underlying mechanisms of its flower coloration remain unclear. In this study, seven complementary DNA (cDNA) clones of genes involved in flavonoid biosynthesis, including chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3′-hydroxylase (F3′H), flavonoid 3′,5′-hydroxylase (F3′5′H), dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase (ANS), were isolated and characterized. Moreover, expression patterns of these seven genes and pigment profiles were investigated across four N. nucifera cultivars with different flower colors: Zhongguohongbeijing [ZGH (red)], Xinghuafen [XHF (pink)], Molingqiuse [MLQS (yellow)], and Zhufengcuiying [ZFCY (white)]. Real-time quantitative polymerase chain reaction (qRT-PCR) analysis showed that during flower development, transcripts of early biosynthetic genes (NnCHS, NnCHI, and NnF3H) were abundant at the early stage; noticeably, highest expression of NnCHI in MLQS probably induced abundant anthoxanthin synthesis and displayed yellow. Expression of late biosynthetic genes, especially NnDFR and NnANS, was generally consistent with change patterns of anthocyanins in ZGH and XHF, but NnF3′H was barely detectable in the pink cultivars. Meanwhile, negligible expression of NnDFR and NnANS was detected in MLQS and ZFCY, respectively, which blocked their colored anthocyanin biosynthesis. Spatial expression analysis revealed that most flavonoid biosynthetic genes were highly expressed in floral tissues, rather than leaves. These results suggest that in N. nucifera cultivars with different flower colors, flavonoid biosynthesis is differentially regulated by the expression of these flavonoid biosynthetic genes, among which, NnCHI, NnF3′H, NnDFR, and NnANS are supposed to be critical for pigment accumulation, and therefore, affect different flower coloration.

Lighting strategies for morphological and physiological characteristics of horticultural crops often focus on the proper daily light integral (DLI); however, a suitable combination of photosynthetic photon flux density (PPFD) and photoperiod at the same DLI is conducive to optimize the light environment management in vegetable seedling production. In the present study, cucumber seedlings (Cucumis sativus L. cv. Tianjiao No. 5) were grown for 21 days under six different combinations of PPFD and photoperiod at a constant DLI of 11.5 mol⋅m⁻²⋅d⁻¹, corresponding to a photoperiod of 7, 10, 13, 16, 19, and 22 h⋅d⁻¹ provided by white light-emitting diodes (LEDs) under a controlled environment. Results showed that plant height, hypocotyl length, and specific leaf area of cucumber seedlings decreased quadratically with increasing photoperiod, and the opposite trend was observed in seedling quality index of cucumber seedlings. In general, pigment content and fresh and dry weight of cucumber seedlings increased as photoperiod increased from 7 to 16 h⋅d⁻¹, and no significant differences were found in fresh and dry weight of shoot and root as photoperiod increased from 16 to 22 h⋅d⁻¹. Sucrose and starch content of cucumber leaves increased by 50.6% and 32.3%, respectively, as photoperiod extended from 7 to 16 h⋅d⁻¹. A longer photoperiod also led to higher cellulose content of cucumber seedlings, thus improving the mechanical strength of cucumber seedlings for transplanting. CsCesA1 relative expression level showed a trend similar to cellulose content. We propose that CsCesA1 is the key gene in the response to cellulose biosynthesis in cucumber seedlings grown under different combinations of PPFD and photoperiod. In summary, prolonging the photoperiod and lowering PPFD at the same DLI increased the quality of cucumber seedlings. An adaptive lighting strategy could be applied to increase seedling quality associated with the reduction of capital cost in cucumber seedling production.