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. 2024 Feb 9;24(1):97.
doi: 10.1186/s12870-024-04793-3.

Carbon monoxide is involved in melatonin-enhanced drought resistance in tomato seedlings by enhancing chlorophyll synthesis pathway

Yunzhi Liu  1 , Junrong Xu  1 , Xuefang Lu  1 , Mengxiao Huang  1 , Yuanzhi Mao  1 , Chuanghao Li  1 , Wenjin Yu  1 , Changxia Li  2
Affiliations

Carbon monoxide is involved in melatonin-enhanced drought resistance in tomato seedlings by enhancing chlorophyll synthesis pathway

Yunzhi Liu et al. BMC Plant Biol. .

Abstract

Background: Drought is thought to be a major abiotic stress that dramatically limits tomato growth and production. As signal molecule, melatonin (MT) and carbon monoxide (CO) can enhance plant stress resistance. However, the effect and underlying mechanism of CO involving MT-mediated drought resistance in seedling growth remains unknown. In this study, tomato (Solanum lycopersicum L. 'Micro-Tom') seedlings were used to investigate the interaction and mechanism of MT and CO in response to drought stress.

Results: The growth of tomato seedlings was inhibited significantly under drought stress. Exogenous MT or CO mitigated the drought-induced impairment in a dose-dependent manner, with the greatest efficiency provided by 100 and 500 µM, respectively. But application of hemoglobin (Hb, a CO scavenger) restrained the positive effects of MT on the growth of tomato seedlings under drought stress. MT and CO treatment promoted chlorophyll a (Chl a) and chlorophyll a (Chl b) accumulations. Under drought stress, the intermediate products of chlorophyll biosynthesis such as protoporphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-Proto IX), potochlorophyllide (Pchlide) and heme were increased by MT or CO, but uroporphyrinogen III (Uro III) content decreased in MT-treated or CO-treated tomato seedlings. Meanwhile, MT or CO up-regulated the expression of chlorophyll and heme synthetic-related genes SlUROD, SlPPOX, SlMGMT, SlFECH, SlPOR, SlChlS, and SlCAO. However, the effects of MT on chlorophyll biosynthesis were almost reversed by Hb.

Conclusion: The results suggested that MT and CO can alleviate drought stress and facilitate the synthesis of Chl and heme in tomato seedlings. CO played an essential role in MT-enhanced drought resistance via facilitating chlorophyll biosynthesis pathway.

Keywords: Carbon monoxide; Chlorophyll synthesis; Drought stress; Genes expression; Melatonin.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Effects of different concentrations of PEG (0, 1%, 5%, and 10%) on root length (a) and plant height (b) of tomato seedlings. Photographs (c) showed the tomato seedlings were incubated in the Hoagland solution containing different concentrations of PEG for 7 days. The data are the average of three replicates and are presented as means ± SE. Different letters indicate significant differences at P < 0.05 according to Duncan’s multiple range tests
Fig. 2
Fig. 2
Effects of different concentrations of MT (0, 10, 50, 100, and 200 µM) on root length (a) and plant height (b) of tomato seedlings under drought stress. Photographs (c) showed the tomato seedlings were incubated in the mixture of Hoagland solution and 5% PEG containing different concentrations of MT for 7 days. The data are the average of three replicates and are presented as means ± SE. Different letters indicate significant differences at P < 0.05 according to Duncan’s multiple range tests
Fig. 3
Fig. 3
Effects of different concentrations of hemin (0, 100, 500, 1000, and 2000 µM) on root length (a) and plant height (b) of tomato seedlings under drought stress. Photographs (c) showed the tomato seedlings were incubated in the mixture of Hoagland solution and 5% PEG containing different concentrations of hemin for 7 days. The data are the average of three replicates and are presented as means ± SE. Different letters indicate significant differences at P < 0.05 according to Duncan’s multiple range tests
Fig. 4
Fig. 4
Effects of MT, CO, MT + CO, and MT + Hb on root length (a) and plant height (b) of tomato seedlings under drought stress. Photographs (c) showed the tomato seedlings treated by 7 days. The data are the average of three replicates and are presented as means ± SE. Different letters indicate significant differences at P < 0.05 according to Duncan’s multiple range tests
Fig. 5
Fig. 5
Effects of MT, CO, MT + CO, and MT + Hb on the levels of Uro III (a), Proto IX (b), Mg-Proto IX (c), Pchlide (d) and the expression of SlUROD(e), SlPPOX(f), and SlMGMT (g) in tomato seedlings under drought stress. The data are the average of three replicates and are presented as means ± SE. Different letters indicate significant differences at P < 0.05 according to Duncan’s multiple range tests
Fig. 6
Fig. 6
Effects of MT, CO, MT + CO, and MT + Hb on the level of heme (a) and the expression of SlFECH(b) in tomato seedlings under drought stress. The data are the average of three replicates and are presented as means ± SE. Different letters indicate significant differences at P < 0.05 according to Duncan’s multiple range tests
Fig. 7
Fig. 7
Effects of MT, CO, MT + CO, and MT + Hb on the levels of Chl a, Chl b, and total Chl (a) and the expression of SlPOR(b), SlChlS(c), and SlCAO(d) in tomato seedlings under drought stress. The data are the average of three replicates and are presented as means ± SE. Different letters indicate significant differences at P < 0.05 according to Duncan’s multiple range tests
Fig. 8
Fig. 8
CO mediates MT-enhanced chlorophyll biosynthesis in tomato seedlings under drought stress. CO is involved in the MT-improved biosynthesis of chlorophyll and heme by increasing content of Proto IX, heme, Mg-Proto IX, Pchlide, Chl a and Chl b and up-regulating expression of SlUROD, SlPPOX, SlFECH, SlMGMT, SlPOR, SlChlS, and SlCAO. CO, carbon monoxide; MT, melatonin; Uro III, uroporphyrinogen III; Proto IX, protoporphyrin IX; Mg-Proto IX, Mg-protoporphyrin IX; Pchlide, potochlorophyllide; Chl a, chlorophyll a; Chl b, chlorophyll b
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