Óxido nítrico na morfofisiologia e qualidade de beterraba sob estresse hídrico

Abstract

Drought is a climatic phenomenon that affects the production of various crops worldwide, such as beetroot, a functional food rich in nutrients, sugars, and bioactive compounds. Considering the potential of nitric oxide (NO) in mitigating water stress and improving postharvest quality of other species, the exogenous application of NO donors, such as sodium nitroprusside (SNP), represents an important strategy for beetroot cultivation. Thus, the objective of this study was to evaluate the effects of SNP on the morphophysiology and post-harvest quality of beetroot subjected to different levels of water stress. For this purpose, the morphophysiology of beetroot plants sprayed with 100 µM SNP or water (control) was evaluated at 36 and 66 days after sowing (DAS), corresponding to two stages of development (young seedlings and adult plants, respectively). Until 36 DAS, the seedlings were subjected to three irrigation levels: 80% of pot capacity (well-watered); 15% of pot capacity (moderate water stress); and severe water restriction from 15 to 36 DAS. After this period, the plants were subjected to four irrigation levels: 80% of pot capacity, 15% of pot capacity, severe water restriction from 15 to 36 DAS followed by re-irrigation (36 to 66 DAS), and late water restriction from 45 to 66 DAS (late severe water stress). During these stages, gas exchange, total chlorophyll content, chlorophyll fluorescence, electrolyte leakage, water content, and seedling growth were evaluated. At 66 DAS, the roots of plants irrigated with 80% and 15% of pot capacity were collected and stored for evaluation of the following post-harvest quality attributes: root yield, sugar production, reducing sugars, nonreducing sugars, proteins, lipids, ash content, root water content, soluble solids, titratable acidity, pH, vitamin C, phenolics, total betalains, betacyanins, betaxanthins, and antioxidant capacity. The results showed that moderate (15% pot capacity) and severe (total restriction) water stresses reduced beetroot growth and photosynthetic capacity, while re-irrigation completely reversed the negative effects of drought. On the other hand, SNP application reversed the effects of moderate stress, mainly due to an increase in carboxylation efficiency and photochemical efficiency. However, SNP was not effective in mitigating severe stress. Regarding post-harvest quality, drought reduced root yield and sugar content but increased the production of bioactive compounds and the antioxidant capacity of beetroot, while SNP application mitigated the negative effects of drought and increased the content of vitamin C and antioxidant capacity regardless of water stress. Taken together, these results indicate that SNP application mitigated moderate water stress in beetroot plants, also improving their post-harvest quality.