Supplementary file 1_Screening for cold tolerance resources in maize seedlings and analysis of leaf cell responses.xlsx

Using 63 maize varieties as materials, this study employed indoor low-temperature stress testing methods to evaluate cold tolerance during the seedling stage. The aim was to investigate the low-temperature resistance of different maize varieties during the seedling stage and to conduct photosynthetic physiological analysis and leaf cell responses for extreme materials. The results of the experiment indicate that: (1) Different maize varieties exhibit variations in cold tolerance during the seedling stage, and the extent to which various measurement indicators are affected by low-temperature stress differs. (2) The comparative analysis of phenotypic traits and physiological indexes showed that low temperature stress inhibited the growth of plant height and stem diameter, and had a great impact on leaf width and leaf area. The relative conductivity and MDA content showed an upward trend and showed a very significant difference. (3) Correlation analysis shows that phenotypic traits and physiological indicators under normal temperature and low-temperature stress have different correlations. (4) Principal component analysis (PCA) transformed the 12 measurement indicators into 7 independent indicators, with a cumulative contribution rate of 87.12%. Leaf area, SOD, stem thickness, relative conductivity, proline content, CAT, and chlorophyll content were identified as the primary evaluation indicators for cold resistance in maize seedlings. (5) Using the membership function method combined with cluster analysis, the cold tolerance of the 63 maize varieties was classified into five categories: extremely strong cold tolerance, strong cold tolerance, moderate cold tolerance, weak cold tolerance, and cold-sensitive. Based on the ranking by D value, two extreme materials were identified: the variety with extremely strong cold tolerance is No. 11 (Jiuyang 818), and the cold-sensitive variety is No. 6 (JR288). (6) Phenotypic observations and measurements of photosynthetic physiological indicators in the two extreme materials revealed that the variety with extremely strong cold tolerance, Jiuyang 818, exhibited more robust plant growth and stronger photosynthetic capacity. (7) Cytological observations of maize leaves revealed that Jiuyang 818 exhibited best cold tolerance during the low temperature stress phase, but JR288 showed significant wilting of leaves six days after low-temperature stress. This finding is consistent with the phenotypic observations and photosynthetic physiological determination results obtained in the preliminary studies. Through indoor identification methods, this study screened and characterized different maize varieties to identify cultivars with varying levels of low-temperature tolerance. The research elucidates the effects of low-temperature stress on photosynthetic physiology and associated changes in leaf cellular structure. These results may provide theoretical references for future studies on low-temperature stress tolerance.

本研究以63个玉米品种为试验材料，采用室内低温胁迫试验方法开展苗期耐寒性评价。本研究旨在探究不同玉米品种的苗期低温抗性，并针对极端材料进行光合生理分析与叶片细胞响应研究。实验结果如下：
(1) 不同玉米品种的苗期耐寒性存在显著差异，且各项测定指标受低温胁迫的影响程度各不相同。
(2) 表型性状与生理指标的对比分析显示，低温胁迫抑制了株高与茎粗的生长，对叶宽和叶面积的影响尤为显著。相对电导率与丙二醛（MDA）含量均呈上升趋势，且差异达到极显著水平。
(3) 相关性分析表明，常温与低温胁迫下的表型性状及生理指标之间存在不同程度的相关性。
(4) 主成分分析（PCA）将12项测定指标整合为7个独立主成分，累计贡献率达87.12%。最终筛选出叶面积、超氧化物歧化酶（SOD）、茎粗、相对电导率、脯氨酸含量、过氧化氢酶（CAT）及叶绿素含量作为玉米苗期耐寒性的主要评价指标。
(5) 采用隶属函数法结合聚类分析，将63个玉米品种的耐寒性划分为5个等级：极强耐寒型、强耐寒型、中等耐寒型、弱耐寒型与低温敏感型。通过D值排序筛选出两份极端材料：耐寒性极强的品种为11号（九阳818），低温敏感品种为6号（JR288）。
(6) 对两份极端材料的表型观察与光合生理指标测定结果显示，耐寒性极强的九阳818植株生长更为健壮，光合能力更强。
(7) 玉米叶片的细胞学观察结果表明，低温胁迫期间九阳818的耐寒性最佳，但JR288在低温胁迫6天后叶片出现明显萎蔫。该结果与前期研究中的表型观察及光合生理测定结果一致。
本研究通过室内鉴定手段，筛选并表征了不同耐寒性等级的玉米品种，阐明了低温胁迫对光合生理的影响以及叶片细胞结构的相关变化。上述研究结果可为未来低温胁迫耐受相关研究提供理论参考。