Plastochron index of 'Cabernet Sauvignon' and 'Chardonnay' grapevines in Fronteira Oeste, in the state of Rio Grande do Sul, Brazil

The objective of this work was to estimate the plastochron index of the 'Cabernet Sauvignon' and 'Chardonnay' grapevine varieties in Fronteira Oeste, in the state of Rio Grande do Sul, Brazil. The experiment was conducted in 2010, in a completely randomized design, using 'Cabernet Sauvignon' and 'Chardonnay' grapevines grown in the municipalities of Itaqui, São Borja, and Maçambará, which were referred to as sites 1, 2, and 3, respectively. Phenological monitoring of the varieties was done from the beginning of sprouting until the pruning of canes (green trimming). The daily thermal sum (dTS, oC day) was calculated using the cardinal temperatures for node appearance in grapevines (10, 25, and 35ºC), whereas the accumulated thermal sum (aTS, oC day) was obtained by adding up the dTS. The plastochron index was estimated by the inverse of the angular coefficient of the linear regression between the number of nodes per cane and aTS. In all three sites, both 'Cabernet Sauvignon' and 'Chardonnay' required degree-days of 10°C and aTS of 810ºC to complete the cycle from the beginning of sprouting until the end of flowering. The estimated plastochron indexes of the 'Cabernet Sauvignon' and 'Chardonnay' grapevines, in Fronteira Oeste, in the state Rio Grande do Sul, were 40.4 and 49.7ºC day per node, respectively.

Phytohormone inhibitor treatments phenocopy brassinosteroid and gibberellin dwarf mutant interactions in maize

Phytohormone biosynthesis produces metabolites with profound effects on plant growth and development. Modulation of hormone levels during developmental events, in response to the environment, by genetic polymorphism, or by chemical application can reveal the plant processes most responsive to a phytohormone. In many cases, chemical inhibitors are applied and the levels of specific phytohormones are measured to determine if, and which, phytohormone is affected by a molecule. In many cases, the sensitivity of biochemical testing has determined multiple pathways affected by a single inhibitor. Genetic studies are not subject to this problem, and a wealth of data about the morphological impacts of hormone biosynthetic inhibition has accumulated through the study of enzyme mutants. We previously identified a complex interplay between brassinosteroid (BR) and gibberellin (GA) in maize, where the interdependence of the two differs dependent on the developmental context. We found that: GA is required for loss of BR to induce retained pistils in the tassel florets (POPIT); BR is required for the loss of GA to induce tiller outgrowth; BR and GA are additive for plant height; BR has no effect on the induction of anther retention in ear florets of GA mutants. In this work, we sought to assess the specificity of three triazole inhibitors of cytochrome P450s by determining their abilities to recapitulate the phenotype of double mutants. The GA biosynthetic inhibitors uniconazole (UCZ) and paclobutrazol (PAC) were applied to the BR biosynthetic mutantna2and all double mutant phenotypes were recovered in the UCZ treatment. PAC was unable to suppress the retention of pistils in the tassels ofnana plant2(na2) mutant plants. The BR biosynthetic inhibitor propiconazole (PCZ) suppressed tiller outgrowth in the GA biosynthetic mutantdwarf5(d5). All treatments were additive with genetic mutants for effects on plant height. Due to additional measurements done here but not in previous studies of the double mutants, we detected new interactions between GA and BR biosynthesis affecting plastochron index and tassel branching. These experiments, a refinement of our previous model, and a discussion of the extension of this type of work are presented.

Growth, fructification and plastochron index of different branches in the crown of the husk tomato (Physalis ixocarpa Brot.)

The husk tomato (<em>Physalis ixocarpa</em> Brot.) is commonly cultivated in Central Mexico for its fruits. The plants of cv. 'Rendidora' show sympodial growth after forming 3-5 internodes in the main axis. From there on, each internode is terminated with a node having one flower bud, one leaf and 2 branches (dichasium type of branching). With the exclusion of the first 3 bifurcations which initiate 4 equal apparent main branches of the plant, each subsequent bifurcation has unequal ramifications: a stronger one which prolongs the apparent main branch, and a weaker one which serves as the origin of an apparent lateral branch. The apparent lateral branches form smaller internodes but these internodes require more time for their growth which is the reason that the plastochron lasts longer in the apparent lateral branches. By forming a smaller number of internodes in the same period of time, the apparent lateral branches reach a lower value of the plastochron index. All apparent lateral branches of a plant produce a greater total number of fruits, but a large proportion of them abscise. Due to this, the harvested fruits come principally from the apparent main branches. The phenology of the husk tomato plant is described. Its short period of development makes possible its cultivation in regions with a limited vegetative period.

Growth of Xanthium (Compositae) internodes at different positions on the stem

Internode growth of vegetative <em>Xanthium</em> plants was studied at various levels on the stem with application of the plastochron index. The bottom internodes were of small size and they displayed small rates of growth. Both, the size of the internodes and their growth rates increased proceeding in the acropetal direction. Rates of cortical cell elongation followed a bell shaped curve, starting with a rate of 7 µm per day, reaching a peak of 15 µm per day and stopping after leaf plastochron index 14. Young internodes, smaller than 25 mm, grew at a constant relative elemental rate of 0.2 day^-1 throughout. Internodes larger than 30 mm displayed an acropetal pattern of elongation.

Chloroplast division during leaf development of Xanthium pensylvanicum Wallr. (Compositae)

Division and growth of chloroplasts was studied during leaf development of <em>Xanthium pensylvanicum</em> at various stages of development represented by the leaf plastochron index.Between leaf plastochron indices -1.00 and 2.56 chloroplast division was observed with little enlargement. Between 2.50 and 5.00 chloroplasts enlarged in diameter with an average rate of 0.21 µm per day. At leaf plastochron index 5.00 chloroplasts attained their mature size of 6.12 µm. No chloroplast division was found after leaf plastochron index 2.50. A change in shape of plastids from spherical proplastids to discoidal accompanied their growth during stages 2.50 and 5.00.

The role of leaf chemistry in Melampsora medusae infection of hybrid poplar: effects of leaf development and fungicide treatment

Immature leaves of poplars are immune to Melampsora leaf rust infection, regardless of the level of resistance or susceptibility of older leaves. Leaf phenolic and protein concentrations were quantified in leaves of varying maturity (measured by leaf plastochron index, LPI) from a rust-susceptible, interspecific hybrid poplar clone, 47-174 (Populus trichocarpa Torr. & Gray × Populus deltoides Bartr. ex Marsh.). Using leaf water extracts and apoplastic solutions, concentrations of phenolics and proteins decreased as LPI increased. Urediniospore germination increased 3-fold, and hyphae elongation increased 3.5-fold as LPI increased from 1 to 11. Inoculation significantly increased concentrations from 9% (LPI 5) to over 120% (LPI 11). Application of triadimefon (Bayleton®) significantly increased the apoplastic concentrations of phenolics and proteins by 43% and 25%, respectively. In vitro urediniospore germination and hyphae elongation decreased over 7-fold and 3-fold, respectively, in these leaves, to levels comparable to immature leaves. This study has shown that defense compounds are present in immature poplar leaves that likely contribute to Melampsora medusae rust immunity, and that triadimefon application created a similar immunity in susceptible leaves. Identification of specific compounds associated with this immunity could assist in the development of resistant poplar clones through traditional breeding or gene modification.

Establishment of a plastochron index for growth assessment of Phalaenopsis

A plastochron index was established for four commercial cultivars of Phalaenopsis: Phalaenopsis 'Taisuco Carol' × (Doritaenopsis 'New Cinderella' × P. 'Isaribi') (Taiwan Sugar Corp., code No. S88-41); Phalaenopsis 'Taisuco Swan' × (P. 'Casablanca Dream' × (P. 'Hohoemi' × P. 'Grace Palm')) (code No. S88-89); Doritaenopsis 'I-Hsin Dreamer' × Phalaenopsis 'Taisuco Harmonylip' (code No. S88-104), and Phalaenopsis aphrodite. The plastochron was based on a 20-mm reference leaf length. Semilogarithmical plots of ln-transformed leaf lengths versus time and linear regression analysis were used to evaluate three criteria of the plastochron index. The results showed that leaves 3–9 of Phalaenopsis aphrodite and leaves 3–8 of the other cultivars grow exponentially (r2 values between 0.90 and 0.97). Therefore, leaves that fulfilled all three criteria for the plastochron index were leaves 3–5 of No. S88-41, leaves 3–4 of No. S88-89, leaves 5–6 of No. S88-104, and leaves 4–5 of Phalaenopsis aphrodite. However the plastochron index can not be used for the slow-growing Phalaenopsis, because two successive leaves could not be measured simultaneously during the exponential phase of leaf development. The average relative growth rate of 0.43 mm/week for Phalaenopsis aphrodite was significantly lower than that of the other three cultivars (0.52 mm/week); plastochron duration also showed significant variation among the four cultivars (P value = 0.0269). In addition, the linear relationship (r2 = 0.97–0.99) of the plastochron index plotted versus time indicates that the intervals between initiation of successive leaves was equal for each of four cultivars. Thus, for these cultivars of Phalaenopsis, leaves that emerge before the reproductive phase can not be fully assessed by the plastochron index.Key words: plastochron index, Phalaenopsis.