Experimental And Modelling Studies On Maize Silk Extension And Its Response To Drought Stress

The silk extension determines the silking time,pollination and fertilisation and is the key index of determining drought tolerance during maize flowering.However,the physiological basis of delayed silking caused by drought stress is still unclear,and there are few studies on dynamic characteristics of silk extension.Therefore,the study of silk extension and its response to drought stress will provide a new strategy for exploring the physiological factors limiting silk extension,and the modeling of silk extension process will be of great significance for understanding the invisible silk extension,silking time,pollination and fertilisation.In this paper,two local summer maize hybrids i.e.An Nong 591(referred as AN591)and Zhong Dan 909(referred as ZD909),which were chosen as the research materials.A field experiment under well-watered(WW,75%±5%field capacity)during the whole growth stage and a pot experiment under well-watered(WW,75%±5%field capacity)during the whole growth stage and drought stress(DS,55%±5%field capacity)from tasseling to silking were carried out at the experimental station in Anhui Agricultural University from 2019 to 2020.Firstly,silk extension characteristics of basal,middle and top silks were investigated.Secondly,the Logistic and segmented models were used to simulate and visualize silk extension.Then,the effects of drought stress on silk extension,sucrose metabolism and related enzyme activities and osmotic regulatory substance content were determined,and the physiological basis of silk extension under drought stress was analysed based on sucrose metabolism.The main results are as follows:i.Under well-watered,silk extension co-developed with leaves and cob,and basal andmiddle silks developed,emergence and senescence earlier than top silk.The Logistic model was used to fit the silk extension and quantify its development process.The results showed that the silk extension was exponential in Phase I and linear in Phase II and III,and the silk extension rate was the maximum around silking,and the thermal time was about 1000 ~oCd.ii.Based on the field experiment data in 2019,a model was established using threeseparate functions to describe the silk extension,and then the model was adjusted and calibrated.Also,the model was independently verified using the field experimental data in2020,which showed that the model was feasible to simulate the silk extension.Finally,the silk extension process in different positions was visualized.Therefore,the silk extension length at different phases can be predicted based on the parameters i.e.linear extension onset(LEO),linear extension rate(LER)and linear extension duration(LED).iii.Under drought stress,silking time was delayed,but anthesis time did not change much,the quality of villi at the tip of silk,cell size and number were affected,the net photosynthetic rate in ear leaves decreased,the contents of sucrose in silk increased while the contents of fructose and glucose decreased,cell wall invertase(CWIN)and sucrose synthetase(SUS)activities in silk decreased while vacuolar invertase(VIN)activity increased,the content of malonaldehyde(MDA)and proline(Pro)also increased significantly.It is preliminarily clarified that the insufficient supply of hexose and the decline of osmotic regulation ability may be the reasons for limiting the silk extension under drought stress.In conclusion,the results showed that drought stress affected sucrose synthesis and hydrolysis,and disrupted the osmotic balance,leading to inhibition of cell expansion,and thus delayed silk extension.In order to adapt to drought stress,maize silks improved osmotic potential through a series of physiological processes to alleviate the effects of drought stress.In addition,the model established in this study can accurately predict the silk extension,which provides a reference for exploring the mechanism model of water-driven silk extension in the future.