Stages Of Apical Development Research Articles

Wood development regulators involved in apical growth in Pinus canariensis.

The shoot apical meristem is responsible of seasonal length increase in plants. In woody plants transition from primary to secondary growth is also produced during seasonal apical growth. These processes are controlled by different families of transcription factors. Levels of transcriptomic activity during apical growth were measured by means of a cDNA microarray designed from sequences related to meristematic activity in Pinus canariensis. The identification of differentially expressed genes was performed using a time-course analysis. A total of 7170 genes were differentially expressed and grouped in six clusters according to their expression profiles. We identified master regulators, such as WUSCHEL-like HOMEOBOX (WOX), to be involved in the first stages of apical development, i.e. growth of primary tissues, while other transcription factors, such as Class III HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP III) and KNOTTED-like (KNOX) and BEL1-like (BELL) HOMEODOMAIN proteins, were found to be induced during last stages of apical seasonal development, already with secondary growth. Our results reveal the main expression patterns of these genes during apical development and the transition from primary to secondary stem growth. In particular, the regulatory factors identified play key roles in controlling stem architecture and constitute candidate genes for the study of other development processes in conifers.

Changes in lipid composition during floral development of Brassica campestris

Apical tissues of Brassica campestris, grown under controlled environmental conditions, were analysed for their lipid content. The principal lipids were sterols, phospholipids and sphingolipids. The major sterols were identified as sitosterol, stigmasterol, campesterol and cholesterol, the phospholipids as phosphatidylethanolamine (PE) and phosphatidylcholine (PC), and the sphingolipids as cerebrosides. In the early stages of apical development, unusually high proportions of cholesterol and cerebrosides were found. However, their relative proportions gradually decreased as the apex developed; a concomitant increase in sitosterol was observed. These results suggested a specific association between these lipids and the development of the shoot apex. PE increased steadily during apical development, whereas PC increased more rapidly, but then declined at the later stage. The relative proportion of campesterol increased in the apex during the late stages of development and appeared to be involved in petal formation, which coincided with the decrease in PC.

Changes in apical morphology during floral initiation and development in pyrethrum (Tanacetum cinerariaefoliumL.)

SummaryChanges in apical morphology during floral initiation and development in pyrethrum (Tanacetum cinerariaefolium L.) were investigated by scanning electron microscopy. The sequence of events may be divided into eleven stages of apical development which are distinctive in both morphology and size. The environmental stimulus promoting rapid flower initiation was demonstrated to be vernalization. Flower initiation occurred after four months under non-vernalizing conditions through an autonomous flower induction process. Devernalization was observed under short day (10 h daylength), low photon flux density (200 µmol m2 s−1) conditions. Apices were never observed to revert to vegetative growth after the initiation of the first involucral bract and therefore this was considered to be the developmental stage at which the apex was committed to generative development.

Apex and ear development in relation to the number of grains on the main-stem ears in spring barley (Hordeum distichon)

SUMMARYApex and ear development in nine spring barley genotypes were studied at two sites in southern Spain in 1988. The genotypes were grouped into medium and early types, depending on the time from sowing to anthesis. Medium genotypes had significantly more spikelet primordia than early ones at both sites. Spikelet mortality was similar between genotypes and sites, resulting in a higher final number of grains/ear in the medium than the early genotypes.There was a positive correlation between the maximum number of spikelet primordia and the duration of three stages of apical development: lemma-, stamen- and awn-primordia. Negative correlations were observed between spikelet mortality and the duration of certain developmental phases of the ear.

A new descriptive scale for early reproductive development in Lolium perenne L.

AbstractEarly reproductive development in Lolium perenne L. has been widely used for defining growth stages in spring, and this has been useful in managing seed crops and in trials involving the use of growth retardants.A numerical scale for apical development based on morphological criteria, has been successfully used in research. The scale identifies eleven clearly recognizable stages of apical development, from the vegetative apex through to the immature, but completely‐formed spike. It is intended that the key should be used to identify consistantly precise stages in apical development.

Relationships between time, temperature, daylength and development in spring barley

SummaryThe effects of sowing date on leaf appearance, spikelet initiation and mainstem apical development in spring barley cv. Triumph were investigated in field experiments involving 13 sowings made during the period 22 February to 1 July over the years 1982–1985. Delaying sowing was associated with faster rates and shorter durations of leaf appearance and spikelet initiation and earlier attainment of all stages of apex development. The rates of leaf appearance and spikelet initiation were correlated with daylength at crop emergence although there was evidence that the latter process was also influenced by temperature. The derivation of three models relating the duration of developmental phases to temperature and/or daylength is described. In these models the attainment of successive stages of apical development was assumed to require the perception by the crop of a ‘threshold amount’ (THR) of accumulated temperature (THR(ΣT)) and/or daylength (THR(ΣPT), THR(ΣP)) above certain base values (TbPb). The base values of temperature and/or daylength for each phase were derived as those values which minimized the coefficient of variation of the amounts of accumulated temperature and/or daylength experienced by all 13 sowings. For various developmental phases the model based on temperature gave base values between 0 and 3 °C. The model based on daylength gave base values between 11 and 13 h. In both these models there was a highly significant correlation between observed and expected dates of attainment of various stages of apex development. It is suggested that the derived relationships between temperature, daylength and apical development could be used as an aid in the forward planning of crop management. The model based on temperature and daylength (photothermal time) gave no useful base values and it is concluded that more precise methods of relating development to these factors must be sought.