Effects Of Water Stress On Jujube Peel Structure And Expansion Protein Gene Expression Activity

The phenology period in the area south of the Huaihe River was earlier than the north,and it had the unique advantage of developing fresh edible dates.However,during the period of growth and development of the jujube fruit in the south of the Huaihe River,the rainfall was relatively large and unevenly distributed,and it was prone to cause cracking,which limited the further development of the southern jujube industry.In this study,the crack fruit of ‘Lifu Gongzao’ and the anti-crack fruit of ‘Wanzao No.3’ were used as test materials,they have independent intellectual property rights.We examined the effects of irrigation and fruit soaking treatment on the cortex,anatomy,and relative expression of the expansive protein gene ZjEXP1-6 in different time points after treatment.The main results are as follows:1.The effect of field irrigation and fruit soaking treatment on peel hardness of cracked and anti-crack fruit samples.The texture was used to detect the peel hardness at the upper,middle and down parts of the ‘Lifu gongzao’ and the ‘Wanzao No.3’ at different times after irrigation and fruit-soaking.The results showed that: the same jujube cultivar peel hardness upper< down< middle;Compared with the hardness of the peel at the same site,the ‘Lifu gongzao’ was smaller than the ‘Wanzao No.3’.With the prolongation of irrigation treatment time,the peel hardness of the ‘Lifugongzao’ peeling fruit varieties decreased obviously.And the peel hardness of the upper and middle parts dropped more than down part.After 30 h of irrigation,compared with 0 h,the upper part dropped by 23.04%,and the difference was significant,which is the only part of fruit cracking in the entire fruit peel.The peel in the middle has dropped by 28.25% and the difference is significant.The down peel was dropped by 16.31%,the difference was also significant.However,there was no significant difference in the hardness of the upper,middle and down parts of ‘Wanzao No.3’.After 3 h of fruit soaking,there was no significant difference in the hardness of peel between the upper,middle and down parts of the fruit of ‘Lifu gongzao’,however the hardness of the upper peel was significantly different from that of the middle and down parts of the fruit after irrigation.After 5 h 20 min of fruit soaking,compared with 0 h,the hardness of the upper pericarp of "Lifu Gongzao" increased by 9.32%,and the difference was not significant.The peel in the middle has dropped by 17.60% and the difference is significant.The down peel was dropped by 11.77%,the difference was not significant.With the increase of irrigation time or fruit soaking time,the hardness of the upper,middle and lower parts of "Wanzao No.3" has not changed much.2.Effect of field irrigation and fruit soaking treatment on the microstructure of pericarp of easily crack and anti-crack fruit samples: the paraffin sections were made from the skins of the upper,middle and down parts of the jujube at different stages after irrigation and water soaking.The results showed that ‘Wanzao No.3’ has 6 layers of epidermis cells with closely arranged cells,and the cells are oblong or rectangular.The ‘Lifu gongzao’ has 5 layers of epidermis cells,and the cells are not arranged closely.The cells are round or irregular.When the water was irrigated for 0 h,the epidermal cell thickness of the upper,middle,and down peels of ‘Lifugongzao’ was 51.5 μm,61.5 μm,and 76.6 μm,respectively.The epidermis cell thickness of the upper,middle,and down peels of ‘Wanzao 3’ was 75.3 μm,75.5 μm,and 73.9 μm,respectively.The difference in epidermal thickness between the upper and middle skins is significant.Under irrigation or fruit soaking condition,the epidermal cells of the pericarp absorb water and swell.24 h after irrigation,the epidermal cell thickness of the upper,middle,and down peels of ‘Lifugongzao’ increased by 60.93%,31.24%,and 4.83%,respectively,when compared with that at 0 h.At 30 h,the upper peel of the fruit cracked.At 4 h 40 min after fruit soaking,the thickness of epidermal cells on the upper skin of ‘Lifu gongzao’ increased by 10% relative to that at 0 h,and the epidermis thickness of the middle and down peels did not change significantly.At the time of 5 h 20 min,the peel of the upper part of the fruit cracked.3.The effect of irrigation and fruit soaking treatment on the relative expression of ZjEXP1-6 of ‘Lifu gongzao’ and ‘Wanzao No.3’.The expansion gene ZjEXP1-6 was cloned from ‘Lifugongzao’ and ‘Wanzao 3’ respectively.Homologous analysis showed that the sequence similarity of ZjEXP1-6 between the two varieties was 100%.The qRT-PCR technique was used to determine the relative expression levels of ZjEXP1-6 in upper of ‘Lifu gongzao’ and ‘Wanzao No.3’ at different periods after irrigation and fruit soaking treatment.The results showed that the expression levels of ZjEXP1,ZjEXP2,ZjEXP3,and ZjEXP4 in the upper of “Wanzao No.3” were 36.6,11.0,6.7,and 7.8 times more than that in the peel of ‘Lifu gongzao’ at 24 h after irrigation.ZjEXP6 reached the maximum difference at 12 h after irrigation,and "Wanzao No.3" was 4.5 times more than that of ‘Lifu gongzao’.The expression level of ZjEXP5 in the skin of ‘Lifugongzao’ was basically higher than that of ‘Wanzao 3’.At 3 h after soaking in water,the expression levels of ZjEXP1,ZjEXP2,ZjEXP3,ZjEXP4,and ZjEXP6 in the peels of ‘Wanzao 3’ were 63.6 times,17.7 times,6.85 times,15.4 times,and 29.5 times more than that in the peel of ‘Lifu gongzao’ respectively,which is the maximum difference.Under water stress,the relative expression levels of ZjEXP1,ZjEXP2,ZjEXP3,ZjEXP4,and ZjEXP6 in the skin of ‘Wanzao 3’ basically rose first and then decreased.It is inferred that the expression activity of these 5 expansin genes are closely related to fruit cracking.