Lettuce seedlings rapidly assemble their microbiome from the environment through deterministic processes
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Abstract Plant-associated microorganisms have significant impacts on plant biology, ecology, and evolution. Although several studies have examined the factors driving variations in plant microbiomes, the mechanisms underlying the assembly of the plant microbiome are still poorly understood. In this study, we used gnotobiotic plants to test (i) whether seedlings create a selective environment and drive the assembly of root and leaf microbiomes through deterministic or stochastic processes, and (ii) whether seedlings structure the microbiome that is transferred through seeds using deterministic processes and whether this pattern changes when seedlings are exposed to the environmental microbiome. Our results show that the microbiome of gnotobiotic plants (i.e., inherited through seeds) is not under the selective influence of the host plant but changes quickly when plants are exposed to soil microbiomes. Within one week, plants were able to select microorganisms from the inocula, assemble the root microbiome, and assemble the shoot microbiome. This study supports the hypothesis that plants at early developmental stages might exert strong selective activity on their microbiomes and contribute to clarifying the mechanisms of plant microbiome assembly.In a Leguminous seedling, and probably in most young Dicotyledons, the rapidly growing leaves near the apex of the shoot inhibit the growth of axillary buds (except of those that are very close bebeath them), and they also tend to inhibit the growth of other shoots, if any are present, and subsequently to kill them. But at the same time they promote the elongation of their own shoot below them, and also stimulate its growth in thickness. The question therefore arises how it is that the growing leaves tend to affect other shoots in the opposite way to that in which they affect their own shoot. This question was brought to notice very clearly by experiments previously reported (Snow 1931, b ). For it was found that in a young pea or broad bean plant that possessed two equal shoots springing from the same level, if one of the shoots was deprived of its growing leaves, it was quickly inhibited in growth by the other shoot, and was killed after about 4 weeks. The question therefore arose how it was that the defoliated shoots were inhibited and killed by the intact shoots, of which the rapidly growing leaves are the inhibiting members, whereas the growth of the intact shoots themselves was not inhibited, but increased, by their own growing leaves above them. It was made clear that the explanation must be that the defoliated shoots were differently situated in relation to the growing leaves of the intact shoots; and it was pointed out that they were differently situated in that, firstly, any influence entering them from these leaves must be travelling upwards in them instead of downwards, and, secondly, they were out of the line between the growing leaves and the roots. But there was also a third difference not mentioned previously, for the stimulus for cambial growth, proceeding from the growing leaves of the intact shoots, travelled down those shoots, but did not spread up into the defoliated shoots, since it is unable to travel in the morphologically upward direction.
Lateral shoot
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Shoots of naturally established, foliated red maple ( Acer rubrum L.) and persimmon ( Diospyros virginiana L.) growing in North Carolina were treated with 2,4-dichlorophenoxyacetic acid (2,4-D) or 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) formulations following various shoot management procedures. Shoot management prior to treatment consisted of decapitating or not decapitating shoots at 2 inches above the ground line in May when the plants were 3 to 6 ft high. Herbicidal applications were made to uncut shoots and to resprouts of previously cut shoots at 30 and 60 days after decapitation. Responses measured 10, 14, and 22 months after treatment were percent control or original shoots, percent control of new shoots, shoot height, number of live stems/plant. The original shoot and new shoot values were averaged to provide a total shoot control index. Spraying of previously cut shoots at 30 or 60 days after cutting was more effective than spraying of uncut shoots except for 2,4,5-T applied to persimmon. The average total shoot control index for 2,4-D treated red maple, considering all rates, application dates, and evaluation dates was 82% for previously cut shoots and 56% for uncut shoots while the corresponding heights were 0.9 and 4.2 ft, respectively. For 2,4,5-T-treated red maple, the total shoot control indices were 92% and 78% for previously cut and uncut shoots, respectively, while the corresponding heights were 0.4 and 1.4 ft. For persimmon, there was a net advantage for treating previously cut shoots with 2,4-D, but the reverse was true for 2,4,5-T. The results are consistent with the theoretical behavior of 2,4-D and 2,4,5-T in woody plants outlined as a basis for conducting the study. Alternate explanations of results are proposed and practical implications described.
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Lengths of all parent and current shoots were measured on three 8- to 10-year-old black birch (Betulalenta L.) trees with branches <8 years old. Older branches had more short shoots (<1 cm long) and shorter long shoots (>2 cm long) than younger branches. Parent long shoots produced three to nine basal short shoots. Observations on short-shoot production were consistent with the hypothesis that only buds with adequate nutrition formed long shoots. Three growth rules were developed for a model that simulated individual branch growth: (i) a regression predicting lateral shoot number from each parent shoot length; (ii) probabilities for the number of short shoots produced by a parent shoot based on the total number of current shoots produced per parent shoot; (iii) a regression predicting current shoot length from parent shoot length, current shoot position (longest to shortest), branch age, and main-axis elongation in the current and previous year. Simulations of 81 branches using these rules predicted shoot numbers and total shoot lengths close to those of the actual branches (R 2 = 0.73–0.84).
Betulaceae
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Canopies of heterophyllous trees expand by production of long shoots. We have previously shown in mountain birch ( Betula pubescens ssp. czerepanovii ) that damage to internode leaves within long shoots does not impede shoot growth, indicating that long‐shoot elongation occurs by means of external resources. To study to what extent leaves other than true long‐shoot leaves are necessary for the normal growth of mountain birch long shoots, we simulated herbivore damage to the two basal leaves of shoots (which flush simultaneously with short‐shoot leaves) and the short‐shoot leaves nearest to the long shoot within the branch. Damage to the two basal long‐shoot leaves significantly reduced long‐shoot growth. Additional damage to short‐shoot leaves, situated proximally to the long shoot, did not retard long‐shoot growth any more than damage to basal leaves alone. To determine the extent to which short‐shoot leaves within a large branch are responsible for the pooled long‐shoot production of the branch, we clipped differing proportions of short‐shoot leaves from such branches. We found small but significant reduction in the pooled length of the long shoots of the branch, presumably indicating a limited role in long‐shoot elongation of current photosynthates within the branch. Our experiments indicate that long shoots are not independent modular units in their carbon economy.
Elongation
Betulaceae
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SUMMARY Experiments on harvesting sweet potato as a green vegetable and as a root crop are described. Whole shoots yielded 62% more than shoot tips. Similar total shoot yields were harvested whether tip removal was at two, three or four week intervals. Root yield was decreased by 31 to 48% by removing shoot tips, while removing whole shoots led to root yield decreases of 48 to 62%. Harvesting shoots at two week intervals gave 72% reduction in root yield, compared with 50% with four week intervals. There were fewer and smaller tubers as the frequency of shoot harvests increased. There were varietal differences in response to shoot removal For reasonable yields of both shoot tips and tuberous roots harvesting shoot tips at four week intervals is recommended.
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In order to induce multiple shoots from Chardonny grape(Vitis vinifera)explants,the effects of explants,media,hormone concentrations and dark treatment on the induction of multiple shoots were studied.The shoots were induced only from the stem explants,the induction frequency reached to 17.5%.There was no difference in the average number of shoots a-mong 3 media of MS,NN1969 and B5.The shoots were induced from the stems on the MS medium supplemented with BA and IBA,and there was significant difference in the frequency of shoot induction among different concentration treatments of BA and IBA.However,there was no significant difference in the average number of shoots and most of shoots induced were single shoot,indicated that there was no significant effect of the combination of BA with IBA on the induction of multiple shoots in this study.The significant effect of the combination of BA with NAA on both the induction frequency of shoots and the number of multiple shoots was observed.The highest induction frequency(9.7%)of shoots and the highest average number of shoots(10.1)were induced from the stems on the MS medium supplemented with 3.0 mg·L-1 BA and 0.1 mg·L-1 NAA,the highest number from one stem reached up to 27.The roots were induced from the shoots on the 1/2MS medium supplemented with 0.05 mg·L-1 IAA.
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Abstract Shoots of ‘Cara Mia’ rose ( Rosa hybrida L.) arising from buds higher on the parent shoot become salable more quickly than those arising from lower buds. Those developing above the 10th or below the 6th true leaf are shorter, of smaller diameter and weigh less. Shoot development is also strongly influenced by shoot diameter at the point of origin. Larger parent shoots give rise to shoots that become salable more quickly, are longer, weigh more, and are larger in diameter than those from smaller parent shoots. Buds from larger-diameter shoots are of larger diameter and have more leaf primordia than those from smaller-diameter shoots, but the diameter of their apical dome is not greater.
Primordium
Pruning
Lateral shoot
Apical dominance
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Although it is commonly recommended that shoot tip cultures be initiated from actively growing shoots, it has been demonstrated that shoot tips collected during the period of rapid shoot extension fail to produce shoot proliferating cultures. Shoot tips of Halesia Carolina and Malus `Golden Delicious' were collected at 2 week intervals from budbreak to summer dormancy and placed on medium containing 0, 4.5, 11.0, 22.5 and 44.5 uM benzyladenine (BA) to determine if elevated BA concentrations could overcome seasonal patterns of shoot proliferation potential (SPP). Both species reached maximum SPP 4 weeks post-budbreak (PBB), and exhibited a second window of high SPP during weeks 10 and 12. Elevated BA concentrations failed to overcome poor SPP exhibited by shoot tips harvested 6 to 8 weeks PBB. Shoot tips collected at 10 to 12 weeks PBB responded more favorably to higher exogenous BA concentrations than shoot tips collected at 2, 4, 6, or 8 weeks PBB. It appears as though seasonal fluctuations in SPP involve other endogenous factors in addition to cytokinins.
Malus
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In this study the vegetative growth parameters of normally developed and underdeveloped shoots were compared in an attempt to quantify shoot heterogeneity in a Shiraz/Richter 99 vineyard. A field trial was performed in the Stellenbosch area,Western Cape, South Africa. Comparisons based on certain vegetative growth parameters were made between normally developed and underdeveloped shoots from both shaded and well-exposed canopies. The longer primary shoots of the normally developed shoots matured earlier in the season, with less apparent competition between shoot lignification and grape ripening. Reserves were more evenly distributed in these shoots. Total starch content over the whole shoot was found to be higher in the normally developed shoots, particularly when wellexposed. More and longer secondary shoots occurred on the normally developed shoots than on the underdeveloped shoots. No difference was found in the number of primary leaves (leaves on primary shoots) betweennormally developed and underdeveloped shoots, although the leaf area was much larger in the case of the former. Normally developed shoots had more and larger secondary leaves (leaves on secondary shoots), while all the leaves that developed in the shaded canopies were found to be larger than those in the well-exposed canopies with a higher leaf area:mass ratio. The normally developed shoots seemed to have a greater potential for producing a higher yield, with better quality, than the underdeveloped shoots, as they have a more desirable leaf area composition in addition to a larger total leaf area per shoot.
Vineyard
Vegetative reproduction
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