Regulation of Plant Growth, Photosynthesis, Antioxidation and Osmosis by an Arbuscular Mycorrhizal Fungus in Watermelon Seedlings under Well-Watered and Drought Conditions

Abstract

Drought stress has become an increasingly serious environmental issue that influences the growth and production of watermelon. Previous studies found that arbuscular mycorrhizal (AM) colonization improved the fruit yield and water use efficiency (WUE) of watermelon grown under water stress; however, the exact mechanisms remain unknown. In this study, the effects of Glomus versiforme symbiosis on the growth, physio-biochemical attributes, and stress-responsive gene expressions of watermelon seedlings grown under well-watered and drought conditions were investigated. The results showed that AM colonization did not significantly influence the shoot growth of watermelon seedlings under well-watered conditions but did promote root development irrespective of water treatment. Drought stress decreased the leaf relative water content and chlorophyll concentration, but to a lesser extent in the AM plants. Compared with the non-mycorrhizal seedlings, mycorrhizal plants had higher non-photochemical quenching values, which reduced the chloroplast ultrastructural damage in the mesophyll cells and thus maintained higher photosynthetic efficiency. Moreover, AM inoculation led to significant enhancements in the enzyme activities and gene expressions of superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, and monodehydroascorbate reductase in watermelon leaves upon drought imposition. Consequently, AM plants exhibited lower accumulation of MDA, H2O2 and O2− compared with non-mycorrhizal plants. Under drought stress, the soluble sugar and proline contents were significantly increased, and further enhancements were observed by pre-treating the drought-stressed plants with AM. Taken together, our findings indicate that mycorrhizal colonization enhances watermelon drought tolerance through a stronger root system, greater protection of photosynthetic apparatus, a more efficient antioxidant system and improved osmoregulation. This study contributes to advances in the knowledge of AM-induced drought tolerance.

Improved Drought Tolerance by AMF Inoculation in Maize (Zea mays) Involves Physiological and Biochemical Implications

“…Increased stomatal functioning enhances CO 2 entry into the leaf tissues and its successful assimilation was observed in AMF-inoculated plants, reflected in terms of increased PSII activity; such results have also been reported in AMF-inoculated wheat [73]. Similar to our results, [74] also demonstrated increased photosynthetic performance of watermelon due to AMF inoculation. Stressful growth conditions increase NPQ due to excess accumulation of protons leading to saturation of the electron transport chain [75][76][77].…”

“…Plants tend to mitigate the effects of stresses at the chloroplast level by increasing NPQ so as to dissipate excess excitation energy [69,78]. AMF inoculation regulates Rubisco activity and prevents photoinhibition under drought stress, reflected in considerable amelioration of deleterious effects [74]. Zea mays exposed to drought stress showed an apparent decline in the activity of nitrate reductase and the uptake of N, with more reduction due to severe drought (SD).…”

“…Increased activities of antioxidant enzymes lead to elimination of excessive ROS, thereby preventing damage to structural and functional integrity of cells [71]. Earlier, [74,91] reported significant protection to chloroplast functioning, structure of thylakoids and stomata by lowering of the oxidative damage via up-regulation of the antioxidant metabolism. Up-regulation of the AsA-GSH pathway maintains the ratio of NADP/NADPH, leading to optimization of photosynthetic electron transport.…”

Know your enemy, embrace your friend: using omics to understand how plants respond differently to pathogenic and mutualistic microorganisms

“…During the ingrowth of ectomycorrhizal (ECM) fungi into host plant tissues, for instance, the expression of defense signaling genes and genes coding for hypersensitive-induced response proteins are quickly attenuated (Johansson et al, 2004;Duplessis et al, 2005;Le Quere et al, 2005;Adomas et al, 2008;Plett et al, 2014a;Plett et al, 2015). Studies of early gene regulation during the colonization of host plants by either rhizobial bacteria or arbuscular mycorrhizal fungi (AM fungi) has also been shown to exhibit little induction of plant defense pathways while the accumulation of reactive oxygen species is repressed (Fester and Hause, 2005;Fouad et al, 2014;Benhiba et al, 2015;Mo et al, 2016;Sarkar et al, 2016). The concept that the plant can induce different panels of gene transcription during colonization by beneficial or detrimental microbes is further confirmed by other work studying pathogens and mutualists colonizing the same plant under the same conditions.…”

Mechanism of application nursery cultivation arbuscular mycorrhizal seedling in watermelon in the field

“…These symbioses are especially important in soils with low endogenous P or in stress conditions (Panigrahy et al , ). AMF colonisation increases watermelon yield in drought stress (Mo et al, ). In addition, AMF reduce Fusarium infections in tomato ( Solanum lycopersicum ), Bipolaris sorokiniana disease in perennial ryegrass ( Lolium perenne L.) and nematode infections in pigeon pea ( Cajanus cajan ) (Goswami et al , ; Steinkellner et al, ; Li, Guo, Michael, et al, ).…”