Carbon starvation reduces carbohydrate and anthocyanin accumulation in red-fleshed fruit via trehalose 6-phosphate and MYB27

Kiwifruit (Actinidia spp.) is a recently domesticated fruit crop with several novel-coloured cultivars being developed. Achieving uniform fruit flesh pigmentation in red genotypes is challenging. To investigate the cause of colour variation between fruits, we focused on a red-fleshed Actinidia chinensis var. chinensis genotype. It was hypothesized that carbohydrate supply could be responsible for this variation. Early in fruit development, we imposed high or low (carbon starvation) carbohydrate supplies treatments; carbohydrate import or redistribution was controlled by applying a girdle at the shoot base. Carbon starvation affected fruit development as well as anthocyanin and carbohydrate metabolite concentrations, including the signalling molecule trehalose 6-phosphate. RNA-Seq analysis showed down-regulation of both gene-encoding enzymes in the anthocyanin and carbohydrate biosynthetic pathways. The catalytic trehalose 6-phosphate synthase gene TPS1.1a was down-regulated, whereas putative regulatory TPS7 and TPS11 were strongly up-regulated. Unexpectedly, under carbon starvation MYB10, the anthocyanin pathway regulatory activator was slightly up-regulated, whereas MYB27 was also up-regulated and acts as a repressor. To link these two metabolic pathways, we propose a model where trehalose 6-phosphate and the active repressor MYB27 are involved in sensing the carbon starvation status. This signals the plant to save resources and reduce the production of anthocyanin in fruits.     

Manipulation of flavour and aroma compound sequestration and release using a glycosyltransferase with specificity for terpene alcohols

Glycosides are an important potential source of aroma and flavour compounds for release as volatiles in flowers and fruit. The production of glycosides is catalysed by UDP‐glycosyltransferases (UGTs) that mediate the transfer of an activated nucleotide sugar to acceptor aglycones. A screen of UGTs expressed in kiwifruit (Actinidia deliciosa) identified the gene AdGT4 which was highly expressed in floral tissues and whose expression increased during fruit ripening. Recombinant AdGT4 enzyme glycosylated a range of terpenes and primary alcohols found as glycosides in ripe kiwifruit. Two of the enzyme's preferred alcohol aglycones, hexanol and (Z)‐hex‐3‐enol, contribute strongly to the ‘grassy‐green’ aroma notes of ripe kiwifruit and other fruit including tomato and olive. Transient over‐expression of AdGT4 in tobacco leaves showed that enzyme was able to glycosylate geraniol and octan‐3‐ol in planta whilst transient expression of an RNAi construct in Actinidia eriantha fruit reduced accumulation of a range of terpene glycosides. Stable over‐expression of AdGT4 in transgenic petunia resulted in increased sequestration of hexanol and other alcohols in the flowers. Transgenic tomato fruit stably over‐expressing AdGT4 showed changes in both the sequestration and release of a range of alcohols including 3‐methylbutanol, hexanol and geraniol. Sequestration occurred at all stages of fruit ripening. Ripe fruit sequestering high levels of glycosides were identified as having a less intense, earthier aroma in a sensory trial. These results demonstrate the importance of UGTs in sequestering key volatile compounds in planta and suggest a future approach to enhancing aromas and flavours in flowers and during fruit ripening.     

不同产地‘金圆’猕猴桃低温贮藏下的生理指标及贮藏性变化

以中华猕猴桃(Actinidia chinensis Planch.)黄肉新品种‘金圆’果实为材料,通过低温贮藏实验(1℃±0.5℃,相对湿度90%~95%),系统研究武汉和六盘水所产‘金圆’果实的生理指标及贮藏性。结果显示,两地‘金圆’果实硬度和色彩角(h值)随贮藏时间延长而逐渐下降,硬度在前20 d下降幅度大。果实可溶性固形物(SSC)含量和干物质在贮藏期间变化规律基本一致,六盘水产果实的SSC和干物质含量高于武汉。武汉产果实VC、可溶性总糖、可滴定酸含量仅在80 d时高于六盘水,其他时间均低于六盘水。两地果实的固酸比和糖酸比变化一致,六盘水产果实固酸比(SSC/TA)和糖酸比(SS/TA)在80 d时均达到峰值,而武汉产果实只有糖酸比达到峰值。随贮藏时间延长,两地果实的失重率均缓慢上升,160 d时武汉和六盘水果实的失重率分别为2.82%和2.55%;在贮藏前60 d两地果实腐烂率较低,之后上升较快,160 d时六盘水产果实腐烂率是武汉的1.77倍。本研究结果表明六盘水产‘金圆’果实的风味品质优于武汉,而武汉产果实贮藏性更好些。     

Kiwifruit extracts inhibit cytokine production by lipopolysaccharide-activated macrophages, and intestinal epithelial cells isolated from IL10 gene deficient mice

Inflammatory bowel disease (IBD) is a chronic, inflammatory disorder of the gastrointestinal tract involving an inappropriate immune response to commensal microorganisms in a genetically susceptible host. This study examined the effects of aqueous and ethyl acetate extracts of gold kiwifruit (Actinidia chinensis) or green kiwifruit (Actinidia deliciosa) using in vitro models of IBD. These models comprised primary macrophages and intestinal epithelial cells isolated from C57BL/5J and interleukin-10 gene deficient (Il10^−/−) mice and RAW 264.7, a murine macrophage-like cell line. All four kiwifruit extracts reduced the activation of these models after lipopolysaccharide stimulation, decreasing nitric oxide and cytokine secretion by both Il10^−/− and wild-type cells. The ethyl acetate extracts exhibited the highest anti-inflammatory activity, with almost complete suppression of lipopolysaccharide-stimulated macrophage activation. These results suggest that kiwifruit extracts have significant anti-inflammatory activity relevant to IBD. We suggest that the Il10^−/− mouse is a suitable model for further study of these compounds.     

Green kiwifruit modulates the colonic microbiota in growing pigs

Aims: To investigate whether green kiwifruit modulates the composition of colonic microbiota in growing pigs. Methods and Results: Thirty‐two pigs were fed the control diet or one of the three test diets containing either cellulose, freeze‐dried kiwifruit or kiwifruit fibre as the sole fibre source for 14‐day study. A Ward’s dendrogram of similarity cluster analysis on PCR‐DGGE gels revealed that inclusion of freeze‐dried kiwifruit and kiwifruit fibre into diets altered the bacterial community, indicating the presence of two distinct clusters. Quantification of different bacterial groups by qPCR demonstrated that pigs fed the freeze‐dried kiwifruit or kiwifruit fibre diets had a significantly higher number (P < 0·05) of total bacteria and Bacteroides group and a lower number of Enterobacteria and Escherichia coli group, as well as a greater ratio of Lactobacillus to Enterobacteria when compared to pigs fed the control or cellulose diets. Conclusions: Green kiwifruit, mainly because of fibre, modulated the colonic microbiota, leading to an improved intestinal environment in growing pigs. Significance and Impact of the Study: This is the first report regarding the effect of green kiwifruit on gut microbiota using the in vivo pig model. These results provide the first evidence of interaction between green kiwifruit and colonic microbiota.     

Bis(guanylhydrazones) negatively affect in vitro germination of kiwifruit pollen and alter the endogenous polyamine pool

Bis(guanylhydrazones) are a class of compounds known to interfere with the metabolism of polyamines (PAs). Among them, the methylglyoxal derivative (MGBG) has been studied most thoroughly. Because PAs and their biosynthetic enzymes are strongly involved in pollen tube organization, emergence and elongation, a number of these inhibitors have been studied in the present work for their effects on the in vitro performance of kiwifruit (Actinidia deliciosa) pollen. Increasing concentrations of several bis(guanylhydrazones) in the range 0.05-1 mM were checked for their effect on pollen germination. Most of the compounds tested showed a dose-dependent inhibitory effect on tube emergence, which was established very early during incubation. At 0.5 mM, the methylpropylglyoxal derivative (MPGBG) had a stronger inhibitory effect than MGBG. To verify whether the inhibitors reached their metabolic target, PA levels and S-adenosylmethionine decarboxylase (SAMDC) activity were determined in pollen germinated in the presence or absence (controls) of 0.5 mM bis(guanylhydrazones). Spermidine (Spd) content was significantly reduced in the treated pollen, and this effect was more pronounced after treatment with MGBG than with MPGBG. An early and strong reduction in SAMDC activity was observed after exposure to either inhibitor. Inhibition of pollen germination by MGBG or MPGBG could not be reversed by the addition of exogenous Spd, which per se was inhibitory. Taken together, our results suggest that bis(guanylhydrazones) alter PA metabolism and negatively affect kiwifruit pollen germination, even though a strict cause-effect relationship could not be established, and other mechanisms, unrelated to PA activity, must be involved.     

THE RELATIONSHIP BETWEEN A FLOWER GALL MIDGE PSEUDAS-PHONDYLIA SP. (DIPTERA: CECIDOMYIIDAE) AND ITS HOST PLANT ACTINIDIA VALVATA*

Abstract Kiwifruit plants, Actinidia sp., are native to subtropical China. The flower-bud gall of A. valvata, which is induced by an undescribed gall midge in the genus Pseud as phond ylia, is valued by the pharmaceutical industry. When studying the biology of the Actinid ia/Pseud as phond ylia interaction in Central-south China we found evidence suggesting that under certain circumstances the gall insect modifies the reproductive mode of the dioecious host plant. Surveys and field experiments in the National Hupingshan Natural Reserve showed a high frequency of galled trees. The density of galled trees varied among valleys and among trees within the valleys. In two valleys, 92% and 75%, respectively, of all trees were attacked, while in a third valley no trees were attacked. When infested, staminate tree only produced galls, whereas pistillate plants produced normal fruits as well as galls. Gall shape differed between male and female trees. Trees with galls tended to produce more fruits than treea without galls. We speculate that this is one of a few documented examples of an insect that induces androdioecy in an otherwise functionally dioecious plant.     

Kiwifruit micropropagation through callus shoot-bud induction

Summary A profitable system for the establishment of morphogenic callus cultures and indirect shoot induction and development was accomplished from nodal shoot segments obtained from adult and micropropagated plants of kiwifruit (Actinidia deliciosa [Chev.] Liang and Ferguson, var.deliciosa) cv. “Hayward”. The effects of medium composition, cytokinin levels, dilution of salts, and type of callus derived from the cultured primary explants were studied. Medium composition as well as type of callus greatly affected organogenic responses.