Objective The study was conducted to explore the effects of weak light on tomato plant growth and physiological indicators, screen weak light tolerant materials, with a view to providing a basis for cultivating weak light tolerant tomato varieties.

Method To clarify the effects of weak light on the growth and development of tomatoes and their mechanisms of weak light tolerance, the study was conducted on plant growth indicators, chlorophyll content, chlorophyll fluorescence parameters, and antioxidant enzyme activity in the weak light tolerant tomato inbred line 'GC303' and the weak light sensitive inbred line 'LA2838' under artificial climate conditions, with 500 μmol/m²·s light intensity as the control and 100 μmol/m²·s light intensity as the weak light treatment.

Result Under normal light conditions, the dry and fresh weights of the 'LA2838' were significantly higher than those of the 'GC303'. Under weak light stress treatment the growth of biomass such as dry and fresh weights of 'LA2838' significantly slowed down compared to 'GC303', with an increase in leaf area and excessive plant growth. In terms of photosynthesis level and photosynthetic pigment content, under normal light conditions, the chlorophyll content of 'LA2838' in the seedling stage was significantly higher than that of 'GC303', and there is no significant difference in photosynthetic indicators. Under weak light treatment, the quenching value of photosynthetic inhibition damage of 'GC303' was significantly reduced. The degree of photooxidative damage was lighter, and the plant's photoprotection was enhanced, and 'GC303' has higher photosynthetic efficiency. In terms of antioxidant enzyme activity and MDA content, under normal light conditions, the SOD and POD activities of 'GC303' were higher than those of 'LA2838', indicating a higher light energy utilization efficiency. Under weak light stress, the activities of SOD, CAT, and POD in 'GC303' leaves were significantly reduced compared with 'LA2838', while MDA showed no significant difference, indicating a stronger peroxide scavenging ability. In terms of transcriptome, compared with 'LA2838', 'GC303' had 1913 differentially expressed genes, including 987 up-regulated genes and 926 down-regulated genes. The differentially expressed genes were significantly enriched in response to plant stress such as abiotic stress, chloroplast movement, metal ion transport, microtubule-based movement, and photosynthetic pathways.

Conclusion Weak light stress has a significant impact on the growth indicators and photosynthetic parameters on weak light sensitive inbred lines and weak light tolerant tomato inbred lines, making it an important indicator for identifying plants' weak light tolerance. However, it has a relatively minor impact on chlorophyll and MDA content indicators.