Yunye Zheng

Association of polyamines in governing the chilling sensitivity of maize genotypes.

Chilling stress is an important constraint of global production of maize. This study was undertaken to compare the chilling responses of different maize seedling tissues and to analyze changes in polyamines as a result of chilling stress. Reponses to chilling were characterized in two maize (Zea mays L.) inbred lines, ‘HuangC’ and ‘Mo17’, that putatively differ in chilling sensitivity. Seedlings were exposed to low temperature (5°C) and chilling injury was estimated by electrical conductivity (EC), malonaldehyde (MDA) concentration, and by changes in putrescine (Put), spermidine (Spd) and spermine (Spm) concentrations in root, mesocotyl, and coleoptile tissues. Membrane permeability (as measured by EC), MDA concentrations and Put concentrations in the three tissue of maize seedlings increased after chilling stress, except for the Put concentration in roots. Spd and Spm concentrations in the three tissues of seedlings decreased after chilling stress. The EC for cold stressed tissues were lower in HuangC than Mo17. Also, the EC of coleoptile tissues were lower than for mesocotyl in both inbred lines. We suggest that mesocotyl tissue can be used to evaluate cold tolerance in maize. Stepwise regression analyses showed that chilling injury in roots was generally correlated with Spd concentration while in the mesocotyl injury was mainly correlated with Put and Spd concentrations. Spermidine and Spm concentrations in the coleoptile were correlated with chilling injury. Characteristics changes of polyamines in chill-tolerant maize seedling combined with regression analysis are a reliable method for evaluating chill tolerance in maize lines.

Responses of Antioxidant Enzymes to Chilling Stress in Tobacco Seedlings

Abstract Chilling is one of the major abiotic stresses limiting yield and quality of many important crops. For better understanding of chilling stress responses in tobacco (Nicotiana tabacum), growth rate and antioxidant enzymes of seedlings in 2 tobacco cultivars, viz., MSk326 (chilling sensitive variety) and Honghuadajinyuan (HHDJY, chilling tolerant variety) at chilling temperature (5÷C) were studied. The results showed that the relative growth rate in chilling period to that in recovery period was significantly higher in roots than that in shoots for both cultivars, suggesting that shoots growth was more easily affected by chilling stress. Chilling stress increased peroxidase (POD) activity and reduced superoxide dismutase (SOD) activity in shoots of HHDJY, and catalase (CAT) activity was little affected. In the roots of HHDJY, chilling stress increased SOD and CAT activities, and had little effect on POD activity. For MSk326, chilling treatment increased SOD activity in shoots and declined CAT activity in roots. MDA concentration in both varieties was increased under the chilling stress, while it was decreased after seedlings were recovered growth for 4 d at normal temperature (25÷C). It showed that tobacco seedlings might have the capacity of recovering from chilling injury for a short term. The relationship between the growth rate and antioxidant enzyme activity was analyzed by stepwise regression. It was found that there was a close relationship between relative growth rate of tobacco seedlings and CAT activity under chilling stress condition and regression equations containing CAT could be used in predicting seedling growth rate of tobacco under chilling stress condition.

An Enhanced Drought-Tolerant Method Using SA-Loaded PAMPS Polymer Materials Applied on Tobacco Pelleted Seeds

Drought is one of the most important stress factors limiting the seed industry and crop production. Present study was undertaken to create novel drought-resistant pelleted seeds using the combined materials with superabsorbent polymer, poly(2-acrylamide-2-methyl propane sulfonic acid) (PAMPS) hydrogel, and drought resistance agent, salicylic acid (SA). The optimized PAMPS hydrogel was obtained as the molar ratio of 2-acrylamido-2-methyl-propanesulfonic acid (AMPS) to potassium peroxydisulfate (KPS) and N, N′-methylene-bis-acrylamide (MBA) was 1 : 0.00046 : 0.00134. The hydrogel weight after swelling in deionized water for 24 h reached 4306 times its own dry weight. The water retention ratio (RR) of PAMPS was significantly higher as compared with the control. It could keep as high as 85.3% of original weight after 30 min at 110°C; even at 25°C for 40 d, the PAMPS still kept RR at 33.67%. PAMPS disintegration ratio increased gradually and reached around 30% after embedding in soil or activated sludge for 60 d. In addition, there were better seed germination performance and seedling growth in the pelleted treatments with SA-loaded PAMPS hydrogel under drought stress than control. It suggested that SA-loaded PAMPS hydrogel, a nontoxic superabsorbent polymer, could be used as an effective drought resistance material applied to tobacco pelleted seeds.

“Intelligent” seed pellets may improve chilling tolerance in tobacco

Tobacco seeds and seedlings often encounter low temperature stress in China. An ‘intelligent’ tobacco seed pellet was developed to improve chilling tolerance by adding thermo-sensitive PNIPAAm-co-BMA (poly(N-isopropylacrylamide-co-butyl methacrylate)) hydrogel. PNIPAAm-co-BMA can detect changes in environmental temperature and change its reticular structure accordingly. In addition, the release rate of salicylic acid (SA) loaded in PNIPAAm-co-BMA hydrogel is changed. Tobacco seeds of two different chilling-tolerant tobacco varieties were pelleted by SA-loaded PNIPAAm-co-BMA, and then the germination characteristics, seedling quality and some physiological parameters of the seeds and seedlings were measured after a chilling stress at 11°C for 5 d. The results showed that the germination percentage (GP), germination index (GI), root length, seedling dry weight and the activities of POD (peroxidase) were significantly increased and the concentration of MDA (malondialdehyde) was significantly decreased in the ‘intelligent’ seed pellets compared with the seeds without SA and PNIPAAm-co-BMA in both varieties. The results showed that the ‘intelligent’ seed pellets had thermo-sensitive traits; they enhanced and prolonged the efficiency and acting time of loaded SA. This indicated that the ‘intelligent’ seed pellets pelleted with SA-loaded PNIPAAm-co-BMA could be used to improve chilling tolerance.

Suppression of LOX activity enhanced seed vigour and longevity of tobacco (Nicotiana tabacum L.) seeds during storage

Abstract The preservation of seed viability and quality in storage is an important trait both for commercial and germplasm usage. To better explore potential mechanisms of tobacco seed deterioration, seed packed in cloth bag (C) and vacuum bag (V) were stored under room temperature (RT) and low temperature (LT, 18°C), and sampled periodically for laboratory testing. Seed stored in low temperature with vacuum bag (LT/V) owned the highest seed vigour after 25 months of storage and in room temperature with cloth bag (RT/C) lost seed vigour and germination ability after 20-month storage. Meanwhile, seed in RT/C notably increased about 5-fold endogenous hydrogen peroxide (H2O2), 4-fold malondialdehyde (MDA) contents, 12-fold Lipoxygenases (LOX) activity and 2-fold the expression of NtLOX3 comparing with LT/V at the end of 15-month storage. In addition, regression analysis indicated that LOX activity was strongly negatively correlated with seed vigour as the R2 value reached 0.970 in RT/C. Furthermore, caffeic acid and catechin, the inhibitors of LOX activity, were applied to tobacco seeds pre-treatment and followed with artificial accelerated aging. Seeds pretreated with inhibitors, especially caffeic acid, reduced LOX activity by 50%, MDA and H2O2 contents by 40% and 20%, respectively, and increased more than 1.2-fold seed vigour and seedling quality comparing with seeds pretreated with H2O after 6-day artificial aging, indicating a better seed storability after artificial accelerated aging. These results suggest that LOX accelerated seed aging, and suppression of LOX activity enhanced seed vigour and viability in accelerated aging tobacco seed, opening new opportunities for effective management of seed germplasm under long-term storage and conservation.