Gao Peng, Dong Jie, Wang Sihan, Zhang Wuhua, Yang Tao, Zhang Jinzhu, Che Daidi
College of Horticulture and Landscape Architecture, Northeast Agricultural University, Harbin, China.
Key Laboratory of Cold Region Landscape Plants and Applications, Harbin, China.
Front Plant Sci. 2022 Jan 17;12:808206. doi: 10.3389/fpls.2021.808206. eCollection 2021.
Thunb. has been explored multi-function in medicinal, edible, cosmetic, ornamental and ecological etc. However, natural populations have recently declined substantially in China, besides of global climate change, this species also has the defect of limiting the reproduction of itself such as the hard-to-release seed dormancy. In this study, only 30% of seeds were viable, and the others were incompletely developed or diseased seeds. Without stratification, morphologically complete viable seeds imbibed water but those seeds could not germinate even after seed husk removal under suitable condition to exhibit a physiological dormancy. After cold (4°C) and warm (18 ± 2°C) stratification, macromolecular substances containing carbon or nitrogen accumulated, and respiration, antioxidant enzyme activity, and gibberellin (GA) /abscisic acid (ABA) and auxin (IAA)/ABA ratios increased significantly in seeds. Water absorption also increased as endocarps softened. Thus, physiological dormancy of seed was broken. Although warm and cold stratification increased separation between endocarp and embryo, the endocarp binding force was removed insufficiently, because only 10.20% of seeds germinated. Therefore, stratified seeds were treated with simulated bird digestion. Then, folds and cracks in loosened endocarps increased permeability, and water absorption rate increased to 64.43% compare to 21.14% in cold and warm stratification treatment. With simulated digestion, 24.20% of radicles broke through the endocarp with plumules and cambiums to develop into seedlings. Thus, the seed dormancy type of is physiological as seeds imbibed water and possessed fully developed embryos with a low growth potential in combination with a mechanical constraint from the endocarp. Cold stratification helped remove physiological dormancy, and additional warm stratification accelerated the process. The optimal stratification treatment was 4°C for 45 days followed by 18 ± 2°C for 15 days. After warm and cold stratification, simulated bird digestion broke the mechanical constraint from the seed covering layers. Based on this research, production of seedlings can be greatly increased to help protect the species from further declines.
香椿在药用、食用、美容、观赏及生态等方面的多功能性已得到广泛研究。然而，中国的自然种群数量最近大幅下降，除全球气候变化外，该物种自身还存在种子休眠难以解除等限制繁殖的缺陷。在本研究中，仅有30%的种子具有活力，其余为发育不完全或患病的种子。未经层积处理时，形态完整且有活力的种子能吸收水分，但即便去除种皮，在适宜条件下这些种子仍无法萌发，表现出生理休眠特性。经过低温（4℃）和高温（18±2℃）层积处理后，种子中含碳或氮的大分子物质积累，呼吸作用、抗氧化酶活性以及赤霉素（GA）/脱落酸（ABA）和生长素（IAA）/ABA的比值显著增加。随着内果皮变软，吸水率也有所提高。由此，种子的生理休眠被打破。尽管低温和高温层积增加了内果皮与胚之间的分离，但内果皮的结合力去除不充分，因为仅有10.20%的种子萌发。因此，对层积处理后的种子进行模拟鸟类消化处理。随后，松动的内果皮上的褶皱和裂缝增加了通透性，吸水率提高到64.43%，而低温和高温层积处理时为21.14%。经过模拟消化，24.20%的胚根带着子叶和形成层突破内果皮发育成幼苗。因此，香椿种子的休眠类型为生理休眠，因为种子能吸收水分，拥有发育完全但生长势较低的胚，同时受到来自内果皮的机械约束。低温层积有助于解除生理休眠，额外的高温层积加速了这一过程。最佳层积处理是4℃处理45天，随后18±2℃处理15天。经过低温和高温层积后，模拟鸟类消化打破了种子覆盖层的机械约束。基于此研究，香椿幼苗的产量可大幅提高，有助于保护该物种避免进一步衰退。
