Developmental Physiology of Sugar-beet: IV. EFFECTS OF GROWTH SUBSTANCES AND DIFFERENTIAL ROOT AND SHOOT TEMPERATURES ON SUBSEQUENT GROWTH

The effects of three growth substances, viz. indol-3yl-aceticacid (IAA), gibberellic acid (GA₃), and kinetin (KIN), and differentialshoot and root temperatures on growth of sugar-beet (Beta vulgarisL.) plants have been studied. IAA, GA₃, and KIN were applied in aqueous lanolin at differentconcentrations (50 ppm to 5000 ppm) to decapitated sugar-beetplants at the eight-leaf stage, one group also having alternateleaves removed. The growth substances significantly increasedthe dry weights of the plants when all the leaves were present,which was mainly explained by the large increase in roots. Thegrowth substances probably stimulated cambial activity and hencethe mobilization of substrates resulting in a bigger root whena relatively large leaf area existed. The failure of the plantsto respond to treatments following the removal of alternateleaves suggests that under such conditions the growth substanceshave hardly any major effect on the production of substrates;rather they influence growth by regulating the movement of substratesby altering the ‘sink strength’ if the supply ofsubstrates is not limiting. It could also be that the rootsproduce sufficient growth substances to maintain half the leavesat maximum expansion and maximum photosynthesis. Treatment withgrowth substances would therefore have little effect. When allthe leaves were present, they are limited by insufficient growthsubstances. All combinations of root and shoot temperatures of 17 and 25°C were imposed on plants decapitated at the eight-leafstage, one group also having each alternate leaf removed. Leaf8 expanded most at shoot and root temperature of 25 °C whereasother leaves had the largest areas at shoot and root temperatureof 17 °. When all the leaves were present root growth wasmaximal at shoot temperature of 17°C and root temperatureof 25 °C, but when alternate leaves were removed maximumroot growth occurred at shoot and root temperatures of 25 °C.Generally, a higher concentration of soluble carbohydrates wasfound in the roots and leaves when either the shoot or rootor both were kept at 17 °C. Concentrations of nitrogen,phosphorus, and potassium in different organs were less at 17°C than at higher shoot or root temperatures and decreasedwith age.     

GROWTH OF THE EMBRYO OF GINKGO BILOBA UNDER EXPERIMENTAL CONDITIONS. III. GROWTH RATES OF ROOT AND SHOOT UPON MEDIA ABSORBED THROUGH THE COTYLEDONS

Ball , Ernest . (North Carolina State Coll., Raleigh.) Growth of the embryo of Ginkgo biloba under experimental conditions. III. Growth rates of root and shoot upon media absorbed through the cotyledons. Amer. Jour. Bot. 46(2) : 130-139. Illus. 1959.—Mature embryos of Ginkgo biloba were grown by inserting the cotyledons into agar medium containing one of the naturally-occurring sugars of the seed. These sugars were utilized at 1, 2, 4, 8 or 16% (w/v). Root growth was best on the sugar-mineral-water media and occurred at its maximum in media containing 4% sugar (ca. 0.25 M). The sugars may be listed as follows in order of decreasing effectiveness in root growth: glucose, sucrose, levulose, raffinose, galactose. Since very different growth rates of roots occurred on media of the same osmotic values when the latter were determined by the various sugars, it is suggested that the root utilized the entire sugar molecule as a unit whether it was mono-, di-, or trisaccharide. Such media were not effective in supporting shoot growth. Outstanding growth of shoots was obtained when either glutamine or coconut milk was placed in the culture medium. It is concluded that root growth can occur at a substantial rate by utilizing sugar and manufacturing organic nitrogen from nitrates. Shoot growth, in contrast, appears to require sources of organic nitrogen such as may be furnished by glutamine or coconut milk. These phenomena are thought to constitute fundamental differences between the metabolism of root and shoot of this embryo. Mannitol caused severe inhibition of growth of both root and shoot. It is probably toxic to this embryo. Indoleacetic acid caused severe inhibitions of growth of both root and shoot at all except the lowest concentrations utilized.     

Ca2+对小麦种根及其根毛生长发育的影响

低浓度的ＣａＣｌ２对小麦种根生长、根毛发生和生长无明显影响,高浓度的ＣａＣｌ２（０．１ｍｏｌ／Ｌ）对种根和根毛生长有抑制作用,但不影响根毛的发生。Ｃａ２＋专一性螯合剂ＥＧＴＡ抑制种根生长和根毛的发生及生长,添加一定浓度的外源ＣａＣｌ２,这种抑制作用可被消除。ＣａＭ抑制剂ＴＦＰ（三氟拉嗪）和ＣＰＺ（氯丙嗪）对种根生长、根毛发生和生长均有抑制作用,添加外源ＣａＭ可减弱或消除这种抑制作用。     

Developmental Physiology of Sugar Beet: I. THE INFLUENCE OF LIGHT AND TEMPERATURE ON GROWTH

Sugar beet plants were grown for 12 weeks from emergence ingrowth rooms at temperatures of 10, 17, 24 and 31 °C and20, 50, 80, and 110 cal visible radiation cm^-2d^-1, and the changeswith time in their dry weight, leaf area, leaf numbers, andstorage root sugar determined. The first stage of growth wasdominated by the development of the shoot, but the storage rootgradually assumed increasing importance and eventually grewat a faster rate and to a greater weight than the shoot. Therelative growth rate and final yield of dry matter of the shootwere greatest at 24 °C and of the root between 17 and 24°C. The relative rate of expansion and the final area ofthe leaf surface were also greatest at 24 °C, whilst therates of production and of unfolding of leaves were greatestat about 17 °C. All these attributes were increased withincreased radiation. Net assimilation rate increased almostproportionately with radiation and was not significantly affectedby temperature.The relationships of total leaf area with plantdry weight, root dry weight with shoot dry weight, and totalleaf number with plant dry weight were scarcely affected bychanges in radiation, but were much influenced by temperature.Plants of the same dry weight generally had bigger roots andsmaller areas of leaf surface as temperatures departed from24 °C and had most leaves at 17 °C. Sugar concentrationsin the storage root were greatest at 17 °C, but the totalamount of sugar was about the same at 17 and 24 °C. Theconcentration of sugar in the storage root depended on rootsize.Thus, temperature affected both the rate and pattern ofdevelopment, and radiation affected the rate but not the patternof development.     

EFFECTS OF CA AND SR ON ZEA MAYS SEEDLING PRIMARY ROOT GROWTH

Either Ca or Sr in a mineral nutrient medium prevented toxic effects of other nutrient ions on aerated primary roots of maize; other monovalent or divalent, cations substituted for Ca did not. Calcium in the complete nutrient solution, or as CaCl₂ alone, stimulated the division of apical meristem cells in these roots, as compared to division in water alone, but Sr did not. However, the replacement of Ca in the nutrient medium by Sr resulted in the development of additional secondary roots, probably in part by decreasing the rate of cell division in the apical meristem of the primary root and thereby diminishing apical dominance.     

Growth and Development in the Young Tomato: II. THE EFFECT OF DEFOLIATION ON THE DEVELOPMENT OF THE SHOOT APEX

In tomato seedlings the effects of high temperature in delayingthe enlargement of the shoot apex and of increasing the numberof leaves produced before flowering, were counteracted by removalof the first two leaves during the early vegetative phase. Inplants grown at 25° C. defoliation was followed by rapidenlargement of the apex and earlier flower initiation, the numberof leaves produced before flowering being reduced to that inplants grown at 15° C. Defoliation of plants grown at 15°C. resulted in only a slight increase in the rate of apicalenlargement, and the time to flowering and number of leaveswere unaffected. Growth analysis showed that at the time ofremoval, the first two leaves were not self-supporting and at25° C. were utilizing a much higher proportion of assimilatetranslocated from the cotyledons than at 15° C. These resultsare considered to support the view that at higher temperatures,the first two leaves compete strongly with the shoot apex forsupplies of assimilate.