Blue Light Improves Photosynthetic Performance during Healing and Acclimatization of Grafted Watermelon Seedlings

Abstract

To investigate the importance of light on healing and acclimatization, in the present study, grafted watermelon seedlings were exposed to darkness (D) or light, provided by blue (B), red (R), a mixture of R (68%) and B (RB), or white (W; 35% B, 49% intermediate spectra, 16% R) LEDs for 12 days. Survival ratio, root and shoot growth, soluble carbohydrate content, photosynthetic pigments content, and photosynthetic performance were evaluated. Seedling survival was not only strongly limited in D but the survived seedlings had an inferior shoot and root development, reduced chlorophyll content, and attenuated photosynthetic efficiency. RB-exposed seedlings had a less-developed root system. R-exposed seedlings showed leaf epinasty, and had the smallest leaf area, reduced chlorophyll content, and suppressed photosynthetic apparatus performance. The R-exposed seedlings contained the highest amount of soluble carbohydrate and together with D-exposed seedlings the lowest amount of chlorophyll in their scions. B-exposed seedlings showed the highest chlorophyll content and improved overall PSII photosynthetic functioning. W-exposed seedling had the largest leaf area, and closely resembled the photosynthetic properties of RB-exposed seedlings. We assume that, during healing of grafted seedlings monochromatic R light should be avoided. Instead, W and monochromatic B light may be willingly adopted due to their promoting effect on shoot, pigments content, and photosynthetic efficiency.

Contrary to Red, Blue Monochromatic Light Improves the Bioactive Compound Content in Broccoli Sprouts

“…In the former, B was also associated with decreased sugar content. In more mature seedlings, instead, the highest soluble carbohydrate content was noted under R, and the lowest under B [18]. These differences may be due to the low duration of sprouting (5 d), as compared to the time needed to produce more mature seedlings (12 d).…”

“…Our results, however, strongly suggest that monochromatic R or R+UVA light ought to be avoided, since they are generally associated with decreased sprout (hypocotyl + cotyledon) metabolite content. In mature seedlings, monochromatic R light has also been associated with a range of undesirable effects, including downward curling of leaf margins (the so-called leaf epinasty), smaller leaf area, and reduced chlorophyll content [18]. Although UVA (320-400 nm) per se has been related to the activation of secondary metabolism, adverse effects were apparent when the optimum dose was exceeded [25].…”

“…Instead, far-red light has been associated with adverse effects on metabolite content [17]. Given the rising application of light-emitting diodes (LEDs) in horticultural practice [6,[18][19][20], the interest in manipulating light quality to improve both productivity and quality is currently expanding [19,20].…”

“…Advanced carbohydrate status has been associated with prolonged postharvest longevity [25]. This status depends on both the carbohydrates available at harvest, and the postharvest photosynthetic activity [18]. Therefore, maintaining photosynthetic activity following harvest appears advantageous in occasions where the produce is exposed to light (e.g., at display) [25].…”

Supplementary Light with Increased Blue Fraction Accelerates Emergence and Improves Development of the Inflorescence in Aechmea, Guzmania and Vriesea

“…Although the beneficial effect of increased light intensity on the above-mentioned aspects is well-documented, limited attention has been devoted to the role of light quality (spectral distribution). With the development of light-emitting diodes (LEDs), it is now readily feasible to manipulate light quality [15,16]. The interest in using this possibility to promote plant growth and external quality traits is currently expanding [17,18].…”