Abstract:

The aim of this work was to clarify the response mechanism of Helianthus tuberosus seedlings to drought stress and re-watering. A pot experiment was conducted in which seedlings of H. tuberosus ‘Qingyu’ were subjected to a drought stress treatment （DS）， a control treatment during rewatering （RCK）， and a re-watering treatment （RW）. Seedlings in the control group （CK） were grown under normal （non-drought） conditions. The growth and physiological characteristics of the seedlings in the CK and treatment groups were measured. The growth morphology （total root length， root projected area， root surface area， average root diameter， number of root tips） and physiological parameters （photosynthesis parameters， chlorophyll fluorescence parameters， contents of photosynthetic pigments， water， saccharides， and osmoregulators， antioxidant enzyme activities， proline-metabolizing enzyme activities） of H. tuberosus seedlings were determined at 7， 14， 21， 28 days of drought stress and at 7 and 14 days of rewatering. The results showed that drought stress significantly inhibited the growth of H. tuberosus， but normal growth was restored by re-watering. Compared with plants in the DS group， those in the RW group showed significantly increased total root length， root surface area， root projected area， average diameter， and root tip number （by 18.18%， 54.36%， 30.35%， 34.51%， and 83.29%， respectively）， and higher chlorophyll a and chlorophyll a+b contents （increased by 19.51% and 19.42%， respectively）. Comparing the RW group with the DS group， the actual optical quantum efficiency and photochemical quenching coefficient were increased by 13.64% and 2.99% respectively， the free water content and relative water content were increased by 1250.00% and 1.34%， respectively， and the bound water content and total water content were increased by 12.84% and 8.99%， respectively. After the re-watering treatment， the water-absorbing ability of H. tuberosus seedlings was restored， allowing for normal growth to resume. Compared with the plants in the RCK group， significantly higher stomatal conductance， transpiration rate， and intercellular CO₂ concentration （increased by 90.27%， 52.24% and 44.75%， respectively） in the RW group； those in the RW group showed higher peroxidase activity and sucrose， fructose， and glucose contents on the 7th day， lower superoxide dismutase activity， catalase activity， proline and soluble protein contents， and higher activities of two enzymes in the proline synthesis pathway； Δ¹-pyrroline-5-carboxylic acid synthase and proline dehydrogenase. This promoted proline decomposition， contributing to the regulation of osmotic balance in H. tuberosus seedlings and the maintenance of normal cell turgor pressure. The results of this study provide a theoretical basis and reference for the practical application of water-saving cultivation techniques for H. tuberosus.

Key words: Helianthus tuberosus, drought stress, re-watering