Heng Zhai

Isolation and characterization of an apple cytosolic malate dehydrogenase gene reveal its function in malate synthesis.

Cytosolic NAD-dependent malate dehydrogenase (cyMDH) is an enzyme crucial for malate synthesis in the cytosol. The apple MdcyMDH gene (GenBank Accession No. DQ221207) encoding the cyMDH enzyme in apple was cloned and functionally characterized. The protein was subcellularly localized to the cytoplasm and plasma membrane. Based on kinetic parameters, it mainly catalyzes the reaction from oxalacetic acid (OAA) to malate in vitro. The expression level of MdcyMDH was positively correlated with malate dehydrogenase (MDH) activity throughout fruit development, but not with malate content, especially in the ripening apple fruit. MdcyMDH overexpression contributed to malate accumulation in the apple callus and tomato. Taken together, our results support the involvement of MdcyMDH directly in malate synthesis and indirectly in malate accumulation through the regulation of genes/enzymes associated with malate degradation and transportation, gluconeogenesis and the tricarboxylic acid cycle.

Polyphenolic Compound and the Degree of Browning in Processing Apple Varieties

Abstract Polyphenolic compound in processing apple ( Malus dornestica Borkh. ) varieties and the relationship between polyphenol content and enzymatic browning were studied to provide reference for raw material selection and processing method optimization. The content of polyphenol compound in 10 processing apple varieties (4 cider and 6 juice varieties) were analyzed using the Folin-Ciocalteu method and HPLC. The degree of browning and the activities of polyphenol oxidase were also studied. The content and proportion of the polyphenol varied depending on the variety. Bitter varieties globally showed a higher polyphenol concentration than sweet or acid varieties. Proanthocyanidins, chlorogenic acid, (+)-catechin, (-)-epicatechin were high-concentrated polyphenols in apple fruits. Phloridzin, the unique polyphenol of apple, was abundant in the bitter variety Frequin rouge fruit. Total polyphenols, proanthocyanidins, (+)-catechin, and phloridzin had higher correlations with browning. The correlation was low between chlorogenic acid and browning. The polyphenolic profiles were correlated with the apple types. Cider apples contained more polyphenol than juice apple varieties. The content of flavan-3-01 has a close relationship with fruit browning.

Analysis of Genetic Diversity of Processing Apple Varieties

Genetic diversity of 18 processing apple varieties and two fresh varieties were evaluated using 12 simple sequence repeats (SSR) primer pairs previously identified in Malus domestica Borkh. A total of 87 alleles in 10 loci were detected using 10 polymorphic SSR markers selected within the range of 5-14 alleles per locus. All the 20 varieties could be distinguished using two primer pairs and they were divided into four groups using cluster analysis. The genetic similarity (GS) of groups analyzed using cluster analysis varied from 0.14 to 0.83. High acid variety Avrolles separated from other varieties with GS less than 0.42. The second group contained Longfeng and Dolgo from Northeast of China, the inherited genes of Chinese crab apple. The five cider varieties with high tannin contents, namely, Dabinette, Frequin rouge, Kermerrien, M. Menard, and D. Coetligne were clustered into the third group. The fourth group was mainly composed of 12 juice and fresh varieties. Principal coordinate analysis (PCO) also divided all the varieties into four groups. Juice and fresh apple varieties, Longfeng and Dolgo were clustered together, respectively, using both the analyses. Both the analyses showed there was much difference between cider and juice varieties, cider and fresh varieties, as well as Chinese crab apple and western European crab apple, whereas juice varieties and fresh varieties had a similar genetic background. The genetic diversity and differentiation could be sufficiently reflected by combining the two analytical methods.

The Relation Between Endogenous Hormones and Late-Germination in Buds of Avrolles Apple

In order to provide the physiological bases for selecting late-germination cultivars that can avoid late frost damage, the very late-germination variety Avrolles (Malus domestica) was used to study the relation between the dynamic changes and balance of endogenous hormones and germination time. The concentrations of endogenous GA3, ABA, IAA, and ZR were determined in buds of Avrolles and Judeline (Malus domestica) from dormancy releasing to germination by capillary electrophoresis. The dynamic changes of endogenous hormones concentration in buds of Avrolles and Judeline were similar; but the magnitude and time of the change were significantly different between the two varieties, especially for GA3. GA3 concentration increased with dormancy releasing, then decreased, and increased again before germination in the two varieties. GA3 concentration in Avrolles was 1.72 times that in Judeline at the first peak, the gap increased to 2.22 times at germination. ZR concentration exhibited a continuous increase trend, but it decreased sharply before germination. ZR accumulation in Avrolles took 36 days longer than in Judeline, the peak value was 44% higher than in Judeline. Before germination, ZR concentration in Avrolles was 2.12 times that in Judeline. The differences between IAA and ABA concentration were relatively small in the two varieties, while the ratios of GA3/ABA and (GA3 + IAA + ZR)/ABA in Avrolles were 2.08 and 1.58 times those in Judeline, respectively. The germination of apple bud was regulated by the endogenous hormones. For the late-germination apple Avrolles, its germination requires higher concentration of GA3 and ZR, which leads to the high ratios of GA3/ABA and (GA3 + IAA + ZR)/ABA.

Dynamic Changes in the Calcium Content of Several Apple Cultivars during the Growing Season

Dynamic changes in calcium content were investigated in eight apple cultivars. The results showed that the calcium concentration in leaves and shoots increased with fruit development. The cultivars displayed only a small difference in the calcium concentration during the early stage of development, the difference became very significant at the late stage of development, especially in shoots. In shoots, for example, calcium content was highest in Starkrimson (19 638.6 mg kg^(-1)) and lowest in Fuji (8751.3 mg kg^(-1)). Calcium concentration was highest in young fruits and was found to decrease with the growth of fruit, and was characterized by a dramatic drop at the rapid expansion stage. There was a significant difference among cultivars. Young Starkrimson fruits contained the highest calcium concentration of 506.52 mg kg^(-1) among cultivars tested, followed by Pink Lady and Fuji. The calcium concentration in mature fruits from high to low is as follows: Starkrimson, Sansa, Pink Lady, Senshu, Gala, Fuji, Red General and New Century. In this study, it was found that eight cultivars continuously assimilated calcium during the whole growing season, especially at the young stage when fruit took up 35-46% of total calcium. The calcium content in fruitlets was low in all cultivars; in the expansion stage, there was rapid absorption of about 30% of total calcium, whereas in the ripening fruit, content of calcium was reduced. The calcium accumulation increased with fruit growth in stalk, similar to that in fruit.

Effects of Partial Rootzone Drying on the Growth of Vitis vinifera cv. Malvasia Grafted on Different Rootstocks

Abstract To lay a biological foundation for rootstocks and alternate irrigation (AI) popularization, the effects of partial rootzone drying (PRD) on the growth of the grapevine Malvasia grafted on different rootstocks were investigated. Biological effects of 112 divided root irrigation on three combinations, i.e., Malvasia/420A, Malvasia/3309C, and Malvasidl 10R, were studied by wood-boxed plants. All the plants were separated into three groups for different irrigation strategies. Mass growth of new root in alternate-irrigated plants was remarkably promoted by about 7.8-22.2% higher than the well- watered ones. However, new shoot growth, especially the internode was reduced by alternate irrigation. The average root-shoot ratio of all the three combinations was increased from 1.1 to 1.46. New root growth and internode length were decreased by fixed partial rootzone irrigation (FI) at different amount, M/3309C at 37.9 and 36.9%, M/llOR at 18.4 and 22.5%, respectively. Total biomass of all the three combinations under FI decreased at the rate of 19.2-34.3% compared with well-watered ones. Water stress adaptation of grapevine mainly depends on rootstock. llOR is more efficient than 3309C and 420A in water stress adaptation. PRD-A1 benefited root growth, thus improved the drought-resistant ability of grapevine.

Stimulation of cyclic electron flow around PSI as a response to the combined stress of high light and high temperature in grape leaves

Changes in cyclic electron flow (CEF) around PSI activity after exposing grape (Vitis vinifera L.) seedling leaves to the combined stress of high temperature (HT) and high light (HL) were investigated. The PSII potential quantum efficiency (Fv/Fm) decreased significantly under exposure to HT, and this decrease was greater when HT was combined with HL, whereas the PSI activity maintained stable. HT enhanced CEF mediated by NAD(P)H dehydrogenase remarkably. Compared with the control leaves, the half-time of P700+ re-reduction decreased during the HT treatment; this decrease was even more pronounced under the combined stress, implying significantly enhanced CEF as a result of the treatment. However, the heat-induced increase in nonphotochemical quenching (NPQ) was greater under HL, accompanied by a greater enhancement in high-energy state quenching. These results suggest that the combined stress of HT and HL resulted in severe PSII photoinhibition, whereas CEF showed plasticity in its response to environmental stress and played an important role in PSII and PSI photoprotection through accelerating generation of the thylakoid proton gradient and the induction of NPQ.

Root temperature regulated frost damage in leaves of the grapevine Vitis vinifera L.: Root temperature regulated frost damage in leaves

Background and Aims Soil temperature is an important factor that regulates the response of shoots to extreme temperature conditions, such as heat stress. Little information is known, however, about the role that soil temperature plays in regulating the response of grapevine leaves to frost. The aim of this work was to explore the effect of soil temperature on the frost resistance of leaves and to comprehensively reveal the potential physiological mechanism. Methods and Results In a pot experiment the roots of grapevine seedlings (Vitis vinifera L. cv. Merlot) were kept warm (WARR, 20°C) or cold (COLR, 0°C) when the leaves were subjected to frost treatment. After frost, the degree of injury to the leaves was recorded, and a frost index was calculated. A non‐targeted metabolomics analysis based on GC‐time of flight/MS of the leaves of WARR and COLR after frost treatment revealed metabolic differences induced by variable root temperature. Severe damage was found in COLR leaves; in contrast, slight frost injury occurred in WARR leaves. Frost treatment at a root zone temperature of 0 and 20°C triggered significant changes in metabolites and metabolic pathways in the leaves of grapevine compared with those of the Control, with more metabolites and metabolic pathways altered in the leaves of WARR than in those of COLR. The relevant pathways in the leaves of WARR and COLR that were significant compared with those of the Control were the citrate cycle (TCA cycle) as well as glycine, serine and threonine metabolism, which are related to carbohydrate metabolism and amino acid metabolism, respectively. Conclusions Soil temperature affected the frost tolerance of the leaves of grapevine. Different metabolic mechanisms in the leaves of grapevine responded to freezing temperature, regulated by the different root zone temperature. Significance of the Study The role that the root zone temperature plays in frost damage in leaves provided an integrative insight to investigate the frost mechanism.

Measurement of grape root firmness and its application to the evaluation of cold hardiness: Grape root firmness for cold hardiness evaluation

Background and Aims In this study, the cutting force and work to cut 12 grape cultivars with different cold hardiness were measured with a texture analyser to examine root firmness and its application to the evaluation of cold hardiness. Methods and Results The transverse cut method involved cutting in a direction perpendicular to vascular orientation, and the longitudinal cut method involved cutting in a direction perpendicular to the transverse cut. The transverse maximum cutting force (MCF) and cutting depth showed a linear relationship, while work of transverse cutting and cutting depth indicated a power function. Dornfelder, Merlot Noir, Tannat, Carmenere and Syrah required the least MCF, Vidal, SO4, 3309C and 101‐14M a moderate MCF, and Chambourcin, Beta and Frontenac the highest MCF. Work classification of the 12 cultivars was consistent with MCF classification. Conclusions The correlation coefficients of cold hardiness and MCF at 2 mm cutting depth was the highest in the transverse cut, and the correlation coefficients of cold hardiness and phloem MCF of 1 mm cutting depth was highest in the longitudinal cut. The root phloem/radius ratio was correlated negatively with MCF and work, yet the correlation between xylem/radius and MCF and work was positive. The exodermis/radius ratio was significantly correlated with the MCF and the work of a transverse section and phloem longitudinal section. Significance of the Study The cross‐sectional cut of 2 mm depth and longitudinal cut of 1 mm depth could distinguish the firmness of different cultivars, and could be considered as the determinant index of cold hardiness.