Comparison Of Adversity Resistance Ability Between The Wild And Cultivated Types Of Purslane Under Some Adversity Stress

Purslane(Portulaca oleracea L.),an annual succulent wild herb plant which blongs to C4 and CAM plant,has been ranked the eighth most common plants in the world.It can prevent cardia-cerebrovascular disease and inhibit harmful bacterias due to its abundant organic nutritions such as omega-3 fatty acids,flavonoids,potassium,norepinephrine,melatonin and so on.It has strong adaptabilities to climate,soil and other environmental conditions and has high resistances to multiple adverse conditions such as drought,high temperature,high humidity,saline and heavy metal etc.There are two types of purslanes in our country,the wild type and the cultivated type.In order to make full use uncultivated lands and lands unsuitable for cultivation and to develop purslane resources,these two types of purslane were used as materials to compare the differences between their growths,photosynthesis,and resistances to drought and environments in stuffed greenhouse and analyzed the adversity resistance mechanisms.These two types of purslane grew in a incubator were compared in their seed germinations,seeding growths and morphological characteristics etc.The wild purslane grows prostrately with small leaves,many tiny stems which is not clear distinguished among main and lateral stems,small flowers,small buds and small seeds,and more buds per plant than that in the cultivated purslane.Cultivated purslane grows erectly with broad leaves,robust stems,big flowers,big buds and big seeds.The comparison results about stomatal and photosynthetic related indices of two types of purslanes grew in the field in summer showed that,both stomata apparatus were paracytic and of similar size,their densities on the upper epidermis were greater than that on the lower epidermis;The stomatal densities and indices of the wild purslane were higher than that of the cultivated purslane(P<0.01),the chloroplast numbers per guard cell and photosynthetic pigments contents in wild purslane were lower than those of the cultivated purslane.Under the conditions with high temperature and strong light,the values of Fv/Fo,Fv/Fm and light saturation point of the wild purslane were higher than those of the cultivated purslane,and the values of qI/NPQ and light compensation point were lower than those of the cultivated purslane.These implied that,the cultivated purslane was less tolerant to strong light and shade than the wild purslane.The decreased photosynthetic rate of the cultivated purslane under strong light maybe due to the decreased intercellular CO2 concentration which caused by their stomatal closure and stomatal conductance reduction.Natural drought method was used to compare the drought resistance of two types of purslane and results showed that wild purslane can tolerate the short-term drought,and the cultivated purslane can tolerate extremely drought for a long time.Although darkening and wilting leaves were found earlier on the cultivated purslane,the fell off of the young leaves on the top and the death were found more later in the cultivated because of its stems'strong water-reserving ability.The thickened leafand increased root activity and stomatal density under drought showed both purslanes adaptation to drought.While the increased relative conductivity,MDA content,Fo and NPQ values and the decreased chlorophyll contents and Fv/Fm value under drought showed that drought stress had the negative effects on the cell membrane and photosynthetic systems.The above effects on the wild purslane were more great implied the wild purslane was less tolerant to the drought stress than the cultivated type.Increased activities of antioxidant enzymes and increased contents of osmotic adjustment substances,such as proline and soluble sugar etc,in both purslanes under drought showed that through removing excess reactive oxygen with the increased antioxidant system ability and through decreasing the water potential and enhancing water retention ability with the increased contents of osmotic regulation substances by both purslanes to adapt to the drought stress.Results of purslanes in stuffed greenhouse which produced an enviroment of high temperature,high humidity in air and drought in soil showed that both types of purslanes grew well in a short term treatment,and some cultivated types died when treatment time extended.This implied that the resistance of the cultivated purslane to the stuffed greenhouse enviroment was lower than that of the wild purslane.During the treatment,the reactive oxygen content,such as O2-and H2O2,and the degree cell membrane damage,showed by the indices of relative conductivity and MDA,in the cultivated purslane was higher than that in the wild purslane.This demonstrated that the damage of reactive oxygen on purslanes was one of the damages caused by the stuffed greenhouse.That the roots' water content and root activity decreased significantly at the later stage indicated that the damage on roots which lead to the ability decline of absorbing water and fertilizer was another damages caused by the stuffed greenhouse.While the wild purslane adapted to the adversity caused by the stuffed greenhouse through promoting transpiration by stomatal opening to lower leaf temperature and to promote water-uptaking,through increasing root activity to promote water and fertilizer absorbing,through improving the contents of osmotic adjustment substances to lower cell water potential and to maintain water content in cells,through increasing the antioxidant enzymes' activity and antioxidants contents to scavenge excessive active oxygen and to reduce the cell damage degrees.In conclusion,the plant morphology and growth potential of the cultivated purslane was better than the wild purslane under normal growth conditions.The wild purslane was more adaptable to the environments such as high light intensity,high temperature,high soil drought and high air humidity.While the cultivated purslane was more adaptable to the extremely dry conditions.Therefore,different types of purslanes should be choosed to grow in different adversities in order to make full use of the adversities and develop purslane resources.