摘要:

Histochemical studies of the chronological sequence involved in the uptake of Al by the primary root ofZea maysL., cv. TX 24, showed the primary sites of Al uptake to be the peripheral cells of the root cap and the mucilagenous secretions surrounding the root. Al spread rapidly through the cells of the root cap but the cap initials were the last cells to be reached. Entry of Al Into the rest of the root was considerably less rapid, and was found to be limited to the outer cortical cells of the root apex. Little evidence could be found of Al reaching actively dividing cell populations of the primary root meristem during the first 20 h of this experiment. The concept of Al acting directly on cell division is consequently questioned. Decapped root experiments implied a protective function for the root cap over the quiescent centre and mitotically active cells of the root. Epidermal cells of the root apex were not an effective barrier to Al. It is postulated that Al uptake is a function of the biochemical properties particularly the presence of acid mucopolysaccharides in the cells involved.S. Air. J. Plant Soil1985, 2: 1–7

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634129

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Histoohemioal and ultrastructural studies of aluminium-induced changes inrootmetabolism and the structure of the cytoplasmic organelles of the root cap indicated that the first observable effect of aluminium involved the migration of secretory vesicles of the Golgi apparatus which was considered indicative of interference by Al in membrane transport. Al also resulted in a reduction in the number of cisternae per dictyosome, disruption of the membranes of the cisternae and secretory vesicles as well as alteration to the appearance of the product elaborated in the secretory vesicles. Changes in the frequency and appearance of the endoplasmic reticulum were also noted. Progressive vacuolation of the cells of Al-treated roots was observed. No alteration to the nuclear structure of the cap initials involving either the appearance of the nuclear membranes, or degree of chromatin condensation could be connected to Al injury during the first 20 h of exposure. Al was shown to affect the pattern and intensity of respiratory activity in the root apex. High levels of respiratory activity were detected in control treatments in cells proximal to the cap/root junction and approximating the location of the quiescent centre. Al treatment was found to have a rapid inhibitory effect on the metabolic activity of these cells.S. Air. J. Plant Soil1985, 2: 8–17

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634130

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Surface (0–20 cm) soils were sampled at 100 m intervals along a 3 km transect through Vertisols derived from dolerite and Ecca group mudstone near Standerton, Transvaal. The two geologically correlated soil bodies, which historically appear to have formed the basis for use of either crusting or self-mulching surface habits as local classification criteria, could be clearly distinguished and compared from two main segments of the transect. Comparison of physical properties suggested that the soil bodies could be separated by the following values of each property, air-water permeability ratio of 63; coefficient of linear extensibility: 10%; modulus of rupture: 70 kPa; liquid limit: 45%; and plastic limit: 24%. The self-mulching, dolerite-derived soils had values generally in excess of these limits, The high MOR values for the latter soils indicate that strong crusting potential and self-mulching behaviour are not mutually exclusive and therefore cannot be used as classification differentiae. It is suggested that an alternative basis for separating the two soil bodies may be sought in a revised definition of the vertic A horizon.S. Afr. J. Rant Soil1985, 2: 18–20

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634131

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

An investigation of water conservation as affected by different primary tillage methods was conducted on a soil of the Doveton series (fine-loamy, mixed, thermic family of Rhodic Paleudults), where a direct sampling technique was used to monitor the soil-water profiles. Soil samples were taken for the period just prior to early winter tillage to two weeks before the maize cropflowered. The resultsshowedthat tillage practices which maintain higher levels of surface residues retained more water than practices which by their mode of soil disturbance leave soil surfaces relatively‘clean’. Measured differences in soil physical properties and possibly also surface residue distribution resulting from tillage were used to explain why reduced tillage systems provided better water conservation.S. Afr. J. Plant Soil1985, 2: 21–26

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634132

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

An investigation of water conservation as affected by different primary tillage methods was conducted on a soil of the Doveton series (fine-loamy, mixed, thermic family of Rhodic Paleudults), where a direct sampling technique was used to monitor the soil-water profiles. Soil samples were takenforthe period just prior to early winter tillage to two weeks before the maize crop flowered. The results showed that tillage practices which maintain higher levels of surface residues retained more water than practices which by their mode of soil disturbance leave soil surfaces relatively‘clean’. Measured differences in soil physical properties and possibly also surface residue distribution resulting from tillage were used to explain why reduced tillage systems provided better water conservation.S. Mr. J. Plant Soil1985, 2: 21–26

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634133

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Veinal chlorosis was induced in the lower leaves of young maize plants following treatment with atrazine (2-chloro-4-ethylamino-6- isopropylamino-s-triazine). An ultrastructural investigation indicated that mesophyll chloroplasts, consisting of grana, thylakoids and stroma showed severe disintegration. The seemingly unaffected bundle sheath chloroplasts with stroma, thylakoids and sometimes a few rudimentary grana which normally only show PS I activity, appeared to transform to mesophyll-type chloroplasts with formation of small granai stacks. The mesophyll chloroplasts became more spherical and various ultrastructural changes became visible. The thylakoid system was destroyed, the granai compartments became swollen and the double-layered membrane broke down, leading to disintegration of the chloroplast. Atrazine had little effect on the bundle sheath chloroplasts except in a few cases where the chloroplast membrane exhibited swellings. At rates of 6 ppm atrazine, or prolonged treatment with 3 ppm atrazine, bundle sheath chloroplasts were devoid of starch granules.S. Air. J. Plant Soil1985, 2: 27–30

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634134

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Evidence seems to indicate that the rainfall in the summer rainfall area of the RSA exhibits an oscillatory nature with a period of 16–20 years. To help maize farmers in planning for a dry or wet cycle the most recent dry (1963–1972) and wet (1973–1981) half-cycles were studied. Results showed that planting dates are not affected significantly. On soils with a high water-holding capacity, target yields should not differ by more than 10% at Potchefstroom, Bethlehem and Cedara. On soils with low moisture-holding capacity, however, the target yields could vary markedly between wet and dry half-cycles and in marginal rainfall areas (e.g. Glen) the risk of failure is high. It is imperative to take both climate and soil factors into consideration to ascertain the risk associated with dryland cropping.S. Afr. J. Plant Soil1985, 2: 31–34

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634135

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Gesonde garssaad en swartpuntgarssaad vanaf verskillende lokaliteite is vergelyk. Die ontkiemingsenergie van gesonde saad was na een maand beduidend beter as die van swartpuntsaad. Na 'n opbergingperiode van twee tot drie maande het geen verskille in ontkiemingsenergie en -kapasiteit meer voorgekom nie. Die a-amilase-aktiwiteit was laer in swart- puntsaad as in gesonde saad. Ontkiemingsenergie en a- amilase-aktiwiteit het verskil tussen monsters vanaf verskillende lokaliteite. Ontkiemingskapasiteit is nie benadeel deur die voorkoms van swartpunt nie. Die resultate dui daarop dat swartpuntsaad wel geskik is vir gebruik as moutgars.S.-Afr. Tydskr. Plant Grond1985, 2: 35–37

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634136

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

A new concept of the formation of textural subsoil lamellae has been developed on the basis of their morphology in aeolian coastal deposits in Natal. It has been concluded that they are initiated somewhere at depth in the profile by a single, partial impediment to the downward movement of clay-size materials. The impediment may or may not be readily observable. Because clay is accumulated at the upper surface of a lamella and lost at the lower surface, the lamella will migrate upwards through the profile although the net movement of day ts downward. After a lamella has departed from the initiating plane, a new lamella will start forming at this level and the process will be repeated. Movement of a lamella upwards will eventually lead to its disappearance at shallow depth in the profile by wasting as the diminishing supply of clay no longer balances the loss Micromorphological data have indicated that large amounts of clay in lamellae occur in a non-oriented fashion. The largest porpor of this clay is illuvial, whereas some may have formed neogeneticallyS Ah J Plant Soil1985. 2: 38–44

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634137

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor