Identification of maize silicon influx transporters

Maize (Zea mays L.) shows a high accumulation of silicon (Si),but transporters involved in the uptake and distribution havenot been identified. In the present study, we isolated two genes(ZmLsi1 and ZmLsi6), which are homologous to rice influx Sitransporter OsLsi1. Heterologous expression in Xenopus laevisoocytes showed that both ZmLsi1 and ZmLsi6 are permeable tosilicic acid. ZmLsi1 was mainly expressed in the roots. By contrast,ZmLsi6 was expressed more in the leaf sheaths and blades. Differentfrom OsLsi1, the expression level of both ZmLsi1 and ZmLsi6was unaffected by Si supply. Immunostaining showed that ZmLsi1was localized on the plasma membrane of the distal side of rootepidermal and hypodermal cells in the seminal and crown roots,and also in cortex cells in lateral roots. In the shoots, ZmLsi6was found in the xylem parenchyma cells that are adjacent tothe vessels in both leaf sheaths and leaf blades. ZmLsi6 inthe leaf sheaths and blades also exhibited polar localizationon the side facing towards the vessel. Taken together, it canbe concluded that ZmLsi1 is an influx transporter of Si, whichis responsible for the transport of Si from the external solutionto the root cells and that ZmLsi6 mainly functions as a Si transporterfor xylem unloading.     

Carbon Balance of Tall Fescue (Festuca arundinacea Schreb.): Effects of Nitrogen Fertilization and the Growing Season

The C balance of a tall fescue sward grown under different ratesof N fertilization in summer, autumn, and spring was calculatedusing models derived from measurements of shoot growth, canopygross photosynthesis, shoot respiration and of C partitioningto the roots. Under the diverse growing conditions associatedwith the seasons and the N fertilization, C utilization forabove- and below-ground biomass accumulation never exceeded39 and 14% of the canopy gross photosynthesis, respectively.Carbon losses attributed to root respiration and exudation,which were estimated by difference between canopy net photosynthesisand total growth, ranged between 3 and 30% of canopy gross photosynthesis.Seasonal differences in shoot growth could be attributed tothe amount of intercepted radiation, the radiation-use efficiencyand the C partitioning to the roots. The effect of N deficiencyon shoot growth can be attributed to its effects on canopy photosynthesis(principally resulting from changes in intercepted photosyntheticallyactive radiation) and C partitioning. In comparison with theeffect on shoot growth, the effect of the N deficiency on thecanopy gross photosynthesis per unit of light intercepted overthe regrowth cycle was limited. It is concluded that most ofthe effect of N fertilization on shoot growth is due to changesin C partitioning which result in faster leaf area developmentand greater light interception.Copyright 1994, 1999 AcademicPress Tall rescue, Festuca arundinacea Schreb., carbon balance, nitrogen, grass, fertilization     

影响虎杖毛状根高频诱导的因素探讨

利用发根农杆菌ATCC15834对虎杖（Reynoutria japonica Houtt．）进行遗传转化,探讨影响其毛状根高频诱导的因素。结果表明：成熟叶片是转化效率较高的外植体,感染10d左右可形成毛状根,平均诱导率为55．66％,诱根密度为4．30。经PCR检测．证实农杆菌Ri质粒中的rolB及tms基因全部转入毛状根中。改良YEB培养液活化菌种后对出根作用小显著;叶片未经预培养而直接进行感染,其出根效果要明显好于经过MS。或利用TDZ预培养处理（P〈0．01）．毛状根平均诱导牢可达到81．84％,诱根密度为7．04;稀释菌液浸泡、超声振荡或微波辐射处理均可促使叶片提前出根．其中以超声处理30s效果最显著（P〈0．01）;感染叶片上表皮向上放置进行共培养有利于毛状根形成。在优化各种转化条件后,虎杖毛状根平均诱导率可提高到97．1％,诱根密度达到11．3。     

Growth of Near-isogenic Wheat Lines Differing in Development--Spaced Plants

The relationship between phenological development in wheat (TriticumaestivumL.) and growth was studied to determine if the switchfrom a vegetative to a reproductive apex increases plant growthrate. Plant partitioning and relative growth rates during vegetativeand pre-flowering reproductive periods were determined in twosets of near-isogenic lines differing in phenological development.Spaced plants were grown in two photoperiods (15 and 10 h) toincrease the range of development rates. Lines within each isogenicset and photoperiod treatment did not differ in whole plantgrowth rate despite large differences in developmental rate.In addition, the partitioning of biomass between roots and shootswas also similar. The transition of the apex from vegetativeto reproductive mostly affected the partitioning of shoot biomassinto leaf (blades) and stems (rest of the shoot). A longer timeto reach floral initiation was associated with the productionof more, and larger, leaves as well as more tillers. This resultedin large differences in leaf area between isolines. However,at the whole plant level, all lines accumulated biomass at thesame rate with time. The early flowering lines compensated fortheir reduced leaf area by having a higher net assimilationrate and were thereby able to maintain the same relative growthrate as their later flowering counterparts.Copyright 1998 Annalsof Botany Company Development, growth, partitioning,Triticum aestivumL., wheat, isolines.     

Regulation of shoot branching patterns by the basal root system: towards a predictive model

This study aimed to underpin the development of a generic predictivemodel of the regulation of shoot branching by roots in nodallyrooting perennial prostrate-stemmed species using knowledgegained from physiological studies of Trifolium repens. Experiment1 demonstrated that the net stimulatory influence from the basalrooted region of the plant on growth of newly emerging axillarybuds on the primary stem decreased as their phytomeric distancefrom the basal root system increased. Experiment 2 found thatat any one time the distribution of net root stimulus (NRS)to the apical bud on the primary stem and all lateral brancheswas fairly uniform within a single plant. Thus, although NRSavailability was uniform throughout the shoot system at anypoint in time, it progressively decreased as shoot apical budsgrew away from the basal root system. Based on these findings,a preliminary predictive model of the physiological regulationof branching pattern was developed. This model can explain thedecline in growth rate of buds on a primary stem as it growsaway from its basal root system but not the rapid progressivedecline in secondary branch development on successive lateralbranches. Thus knowledge of NRS availability to emerging budsis not, by itself, a sufficient basis from which to constructa predictive model. In addition, it seems that the ability ofan emerging bud to become activated in response to its localNRS availability is, at least in part, directly influenced bythe activation level of its parent apical bud. The experimentaltesting of this hypothesis, required for continued developmentof the model, is proceeding. Key words: Axillary bud outgrowth, branch development, bud activation, intra-plant variation, nodal roots, prostrate clonal herbs, root signals, Trifolium repens Received 11 September 2007; Revised 25 November 2007 Accepted 18 January 2008     

Heterogeneity in Water Availability Alters Cellular Development and Hydraulic Conductivity along Roots of a Desert Succulent

Plants of the desert succulent Agave deserti were grown in partitionedcontainers to determine whether heterogeneity in soil moistureleads to differences in cellular development and hydraulic conductivityalong individual roots. Roots from containers with a dry distalcompartment (furthest from the shoot), a wet middle compartment,and a dry proximal compartment had distal regions (includingthe root tips) that were more suberized and lignified in theendodermis and adjacent cell layers than were root regions fromthe wet middle compartment. Proximal root regions about 40 mmfrom the succulent shoot base were also relatively unsuberized,suggesting that both external and internal supplies of waterdelayed tissue maturation. Root segments from wet middle compartmentsand from dry proximal compartments had higher hydraulic conductivitythan did the more suberized root segments from dry distal compartments.Unlike distal root segments from wet compartments, segmentsfrom dry compartments suffered no decrease in hydraulic conductivityafter immersion in mercuric chloride, suggesting that aquaporinactivity diminished for roots during drought. The possible closureof water channels could help limit root water loss to a dryingsoil. The delayed development of suberized cell layers may allowroot regions to maximize water uptake from wet soil patches(such as under rocks), and the relatively immature, absorptiveroot region near the base of the shoot may help A. deserti capturewater from a briefly wetted surface soil. Copyright 2000 Annalsof Botany Company Agave deserti, root plasticity, water uptake, aquaporins, suberization, endodermis, divided pots.     

Transport of shoot- and cotyledon-applied indole-3-acetic acid to Vicia faba root

To clarify the participation of indole-3-acetic acid (IAA) originatingfrom the shoot in root growth regulation and the mechanism ofIAA translocation from shoot to root, the movement of ¹⁴C-IAAwhich was applied to the epicotyl or the cotyledon of Viciafaba seedlings was investigated. The radioactivity of IAA appliedto the cotyledon moved faster to the root tip than that appliedto the epicotyl. On the basis of the effect of 2,3,5-triiodobenzoic acid on IAAmovement, a comparison with ¹⁴C-glucose movement and autoradiographicexamination, the nature of IAA movement was concluded to bepolar transport from the epicotyl to the basal part of the roots,while IAA movement from the epicotyl to the cotyledon, fromthe basal part of roots to the apical part, and from the cotyledonto the epicotyl and to the root took place in the phloem. Theradioactivity from ¹⁴C-IAA applied to the cotyledon accumulatedin lateral root primordia and vascular bundles. These factssuggest that IAA produced in cotyledons may participate in theregulation of Vicia root development. (Received December 21, 1979; )     

The Effect of Phosphorus Nutrition upon the Growth and Morphology of Young Plants of Lolium perenne L.

Genotypes of Lolium perenne were grown in soil of low phosphorusstatus, with and without additional phosphorus. Lack of phosphorusresulted in a great reduction in the number of main roots andin an increase in the length of each individual root. The numberof tillers was also reduced, but to a lesser extent than thenumber of main roots. The dry weight of the root and shoot systemwas reduced to a lesser extent than the numbers of roots andtillers. The effect on root relative to shoot growth variedwith the genotype.     

Respiration Rate of Barley Roots: its Relation to Growth, Substrate Supply and the Illumination of the Shoot

The respiration rate of roots on intact barley plants grownin 16 h light 8 h dark cycles shows an exponential decay inthe dark, rises on re-illumination and there is a transientfall 12–14 h into the photoperiod Roots of plants placedin the dark for up to 48 h show a continued exponential decay,and a rather small fall in soluble carbohydrate levels The respirationof roots excised from predarkened plants does not rise on additionof sucrose to the medium bathing them Respiration rate, measured10 h into the photoperiod, shows a constant relation to rootweight in plants 8–24 days old, during which time rootcarbohydrate content first falls and later rises It is concludedthat root respiration rate is not a simple function of carbohydratesupply from the shoot The importance of root respiration inthe carbon budget of barley plants is evaluated and the levelsof control operating on root respiration rate are briefly discussed Hordeum distichum (L ) Lam, barley, respiration rate, light, carbohydrate     

Influence of Genotype and Mineral Nutrition on the Distribution of Growth within Plants of Lolium perenne L. grown in Soil

Genotypes of Lolium perenne were grown with two levels of fertilizerapplication. Using exponential growth-rates and parameters derivedfrom them, the rate of growth of each genotype was partitionedinto the rates of initiation of new roots and tillers, and thegrowth of the individual roots and tillers after initiation.The growth of the individual roots was further analysed by measuringchanges in diameter and length of the main root, and the growthin the branches of the main root. The genotypes varied in their response to additional mineralnutrition. The greater the increase in the rate of shoot growthfor a genotype, the greater was its increase in the rate oftiller initiation, the smaller was the increase in the sizeof its tillers, and the greater was the decrease in its rateof root relative to shoot growth. Within a population of genotypes growing with the same levelof mineral nutrition, the greater the rate of shoot growth ofa genotype, the greater was the rate of initiation of new tillersand, at a low level of mineral nutrition, the smaller the sizeof tillers. With a higher level of mineral nutrition, the higherthe rate of tiller production, the smaller or larger was tillersize, depending upon environmental factors other than mineralnutrition. At both levels of mineral nutrition, the greaterthe rate of shoot growth, the smaller was the rate of root growthrelative to shoot growth, due to relatively less growth takingplace in the branches of the main root.     

Development of the Hypodermal Casparian Band in Corn and Onion Roots

A hypodermal Casparian band develops 40–50 mm from theroot tip in corn and 30–40 mm from the root tip in onion.In both plants, the endodermal Casparian band matures about20 mm closer to the root tip than the hypodermal Casparian band.Using the apoplastic fluorescent dye, Calcofluor white M2R (CFW),a permeability barrier could be distinguished in the radialwalls of the hypodermis 40–50 mm from the root tip incorn and onion. In progressively younger regions of the roots,CFW was first excluded from the outer tangential hypodermalwalls and the inner tangential epidermal walls, then the radialepidermal walls so that in very young regions only the outertangential epidermal walls were permeated. In contrast to CFW,the symplastic fluorescent dye, uranin, was translocated fromthe epidermis into the stele at all distances tested (5.0–50mm from the root tips). CFW and uranin at a concentration of0.01% proved nontoxic to corn and onion roots on the basis ofroot growth tests. Key words: Zea mays, Casparian band, Hypodermis, Allium cepa     

Characterization of Cd translocation and identification of the Cd form in xylem sap of the Cd-hyperaccumulator Arabidopsis halleri

Arabidopsis halleri is a Cd hyperaccumulator; however, the mechanismsinvolved in the root to shoot translocation of Cd are not wellunderstood. In this study, we characterized Cd transfer fromthe root medium to xylem in this species. Arabidopsis halleriaccumulated 1,500 mg kg^–1 Cd in the shoot without growthinhibition. A time-course experiment showed that the releaseof Cd into the xylem was very rapid; by 2 h exposure to Cd,Cd concentration in the xylem sap was 5-fold higher than thatin the external solution. The concentration of Cd in the xylemsap increased linearly with increasing Cd concentration in theexternal solution. Cd transfer to the xylem was completely inhibitedby the metabolic inhibitor carbonyl cyanide 3-chlorophenylhydrazone(CCCP). Cd concentration in the xylem sap was decreased by increasingthe concentration of external Zn, but enhanced by Fe deficiencytreatment. Analysis with ¹¹³Cd-nuclear magnetic resonance (NMR)showed that the chemical shift of ¹¹³Cd in the xylem sap wasthe same as that of Cd(NO₃)₂. Metal speciation with Geochem-PCalso showed that Cd occurred mainly in the free ionic form inthe xylem sap. These results suggest that Cd transfer from theroot medium to the xylem in A. halleri is an energy-dependentprocess that is partly shared with Zn and/or Fe transport. Furthermore,Cd is translocated from roots to shoots in inorganic forms.     

Responses of nitrate assimilation and N translocation in tomato (Lycopersicon esculentum Mill) to reduced ambient air humidity

The impact of low humidity in ambient air on water relations,nitrate uptake, and translocation of recently absorbed nitrogen,was investigated in 5-week-old tomato (Lycopersicon esculentumMill cv. Ailsa Craig) plants grown hydroponically in a completenutrient solution. Plants were subjected to dry air (relativehumidity 2–4% for 6 h. The transpiration rate increasedseveral-fold and the shoot water content decreased by almost20%, whereas root water content was unaffected. No effect onin vitro nitrate reductase (NR) activity was detected when usingan EDTA-contraining assay buffer. Replacement of EDTA with Mg²⁺revealed a significant decline in shoot NR activity, which suggestsphosphorylation of the enzyme during the stress treatment. Plantswere grown in a split-root system, in which one root half wasfed ¹⁵N-nitrate during the treatment, in order to determinenitrate uptake and translocation of recently absorbed nitrogenin the plants. Uptake of nitrate was substantially inhibited,but the proportion of absorbed ¹⁵N that was translocated tothe shoots was only slightly affected. In untreated plants,71% of the ¹⁵N recovered in roots had been retranslocated fromthe shoots, whereas in plants subjected to stress the deliveryof ¹⁵N from shoots to roots appeared to be completely inhibited.The data show that lowered humidity in air has significant effectson both uptake of nitrate as well as translocation of nitrogenwithin the plants. Some of these effects appear to be commonwith those observed in plants subjected to reduced water potentialsin the root environment and point to the possibility of theshoot water relations being highly influential on nitrogen uptakeand translocation. Key words: Air humidity, nitrate assimilation, nitrate reductase activity, nitrogen translocation, tomato, water stress     

Root Morphology and Nitrogen Uptake of Maize Simultaneously Supplied with Ammonium and Nitrate in a Split-root System

We studied the response of maize (Zea mays L. cv. Anjou 256)to a simultaneous, but separated supply of ammonium and nitrate(localized supply, LS). A split-root system was used to supplyhalf of the roots with ammonium and the other half with nitrate.A homogeneously distributed supply of both nitrogen forms (HS)was the control treatment. Seedlings were grown for 12 d fromthe two-leaf to the three-leaf stage in hydroponics at threepH levels (4, 5·5 and 7). The total N concentration was3 mol m^-3. The split-root system was established by removingthe seminal root system and using only four nodal roots perplant. Total root length and root surface area were recordedautomatically with a modified Delta- T area meter. Other morphologicalroot traits (such as main axis length and diameter, number,density, and length of laterals) were recorded manually. Uptakeof ammonium and nitrate was measured by the depletion of thenutrient solution. As compared with LS, HS was superior in shootand root DM, total root length and root surface area, ammoniumand nitrate uptake and shoot nitrogen concentration, irrespectiveof pH level. This indicates that, also under field conditions,mixed ammonium and nitrate fertilization is only beneficialto plant growth if both N forms are evenly distributed in thesoil. At both HS and LS, ascending pH increased the ammonium:nitrateuptake ratio. At LS, declining pH induced a considerable shiftin the distribution of root DM, root length, and root surfacearea the nitrate-fed compartment.Copyright 1993, 1999 AcademicPress Maize, Zea may L., ammonium, nitrate, pH, root morphology, split-root     

Energetics of Plant Growth Under Anoxia: Metabolic Adaptations of Oryza sativa and Echinochloa phyllopogon

Unlike most plant species, Oryza sativa L. cv. S-201 and Echinochloaphyllopogon (Stev.) Koss germinate and grow under anaerobicconditions. In both species, the radicle or shoot emerged byday 3 when the seeds were germinated in air or N₂. Under eithercondition, shoot and/or root dry weight (d. wt) increased linearlyfrom day 3 to day 7, with a corresponding decrease in seed d.wt. In anaerobically grown O. sativa, d. wt accumulation wasreduced to 7% of that in air whereas d. wt lost from the seedwas reduced to only 37%. No root growth occurred during anaerobicgermination and shoot d. wt accumulation accounted for 10% ofthe d. wt lost from the seed. In E. phyllopogon, d. wt accumulationduring anoxia was 25% of that in air, but loss of d. wt fromthe seed was 44% of the aerobic rate. In air, 48% of the d.wt lost from the seed was converted to shoot or root d. wt.Like O. sativa, E. phyllopogon does not produce a root underN₂, but shoot growth accounted for 27% of the d. wt lost fromthe seed. Thus, either in air or N₂, E. phyllopogon was moreefficient at converting seed reserves to shoot/root structuraldry matter than O. sativa . Based on changes in metabolite pools,O. sativa appeared to shift exclusively to fermentation duringanaerobic growth. In E. phyllopogon, however, fermentation alonecannot satisfy the energy requirement for growth without O₂.Rather, fermentation, coupled with limited tricarboxylic acid(TCA) cycle operation could supply sufficient ATP for growthunder anaerobic conditions. An active oxidative pentose phosphatepathway and lipid synthesis were discussed as important mechanismsfor converting NADH to NAD, a necessary cofactor for fermentationand TCA cycle activity.Copyright 1994, 1999 Academic Press Anaerobiosis, Echinochloa phyllopogon, energetics model, fermentation, mitochondrial activity, Oryza sativa, rice, tricarboxylic acid cycle, watergrass     

Effects of CO2 enrichment and intraspecific competition on biomass partitioning, nitrogen content and microbial biomass carbon in soil of perennial ryegrass and white clover

Seedlings of perennial ryegrass (Lolium perenne L. cv. Parcour)and white clover (Trifolium repens L. cv. Karina) grown at fivedifferent plant densities were exposed to ambient (390 ppm)and elevated (690 ppm) CO₂ concentrations. After 43 d the effectsof CO₂ enrichment and plant density on growth of shoot and root,nitrogen concentration of tissue, and microbial biomass carbon(C_mic) in soil were determined. CO₂ enrichment of Lolium perenneincreased shoot growth on average by 17% independent of plantdensity, while effects on root biomass ranged between -4% and+ 107% due to an interaction with plant density. Since tilernumber per plant was unaffected by elevated CO₂, the small responseof shoot growth to CO₂ enrichment was atributed to low sinkstrength. A significant correlation between nitrogen concentrationof total plant biomass and root fraction of total plant drymatter, which was not changed by CO₂ enrichment, indicates thatnitrogen status of the plant controls biomass partitioning andthe effect of CO₂ enrichment on root growth. Effects of elevatedCO₂ and plant density on shoot and root growth of Trifoliumrepens were not significantly interacting and mean CO₂-relatedincrease amounted to 29% and 66%, respectively. However, growthenhancement due to elevated CO₂ was strongest when leaf areaindex was lowest. Total amounts of nitrogen in shoots and rootswere bigger at 690 ppm than at 390 ppm CO₂. There was a significantincrease in C_mic in experiments with both species whereas plantdensity had no substantial effect. Key words: CO₂ enrichment, intraspecific competition, biomass partitioning, Lolium perenne, Trifolium repens, grassland     

Ionic Relations of Garden Orache, A triplex hortensis L.: Growth and Ion Distribution at Moderate Salinity and the Function of Bladder Hairs

The growth of garden orache, A triplex hortensis was studiedunder conditions of mild NaCl or Na₂SO₄ salinity. Growth, drymatter production and leaf size were substantially stimulatedat 10 mM and 50 mM Na⁺ salts. Increased growth, however, appearedto be due to a K⁺-sparing effect of Na⁺ rather than to salinityper se. The distribution of K⁺ and Na⁺ in the plant revealeda remarkable preference for K+ in the roots and the hypocotyl.In the shoot the K/Na ratio decreased strongly with leaf age.However, the inverse changes in K⁺ and Na⁺ content with leafage were dependent on the presence of bladder hairs, which removedalmost all of the Na⁺ from the young leaf lamina. Measurementsof net fluxes of K⁺ and Na⁺ into roots and shoots of growingAtriplex plants showed a higher K/Na selectivity of the netion flux to the root compared to the shoot. With increasingsalinity the selectivity ratio S_{K, Na}^* of net ion fluxes tothe roots and to the shoots was increased. The data suggestthat recirculation of K⁺ from leaves to roots is an importantlink in establishing the K/Na selectivity in A. hortensis plants.The importance of K⁺ recirculation and phloem transport forsalt tolerance is discussed. Key words: Atriplex hortensis, Salinity, Potassium, Sodium, K⁺ retranslocation, Bladder hairs, Growth stimulation     

A Comparison of Dry Matter Partitioning in Seminal and Adventitious Plants of Trifolium repens L

Trifolium repens has two types of root, one derived from theseed and the adventitious roots derived from the stolon nodes.It has been suggested that these two systems have differentpotentials for supporting growth. This paper presents a comparisonof plants grown on single seedling or adventitious roots anddemonstrates that although the shoot: root ratios for the twotypes differ this may be explained by differing shoot morphologies.Comparison of the lamina: root ratios for the two types of plantproduced no statistically significant differences and it isproposed that the two types of root system do not differ intheir relationship with leaf growth. A mechanism for large diameter‘tap’ root formation is suggested. white clover, Trifolium repens L., adventitious roots, seedling roots, shoot: root ratio     

Inflorescence Initiation and Leaf Size in Some Gramineae

The morphology of successive leaves on the flowering shoot wasstudied in species of Glyceria, Lolium, and Triticum. The bladesof successive leaves were progressively longer, eventually reachinga maximum, after which the blades of the last few leaves producedbefore heading were shorter. When the longest leaf blade waselongating, dissection of the shoot apices showed that inflorescenceinitiation was taking place. Epidermal cell measurements inTriticum indicate that differences in blade length are due todifferences in the amount of cell extension. It appears that a correlated change occurs in blade morphologyassociated with the onset of the reproductive state of the shootapex, brought about via changes in the amount of cell extension. A study of the effect of different amounts of low-temperatureand different day-lengths on the relation between inflorescenceinitiation and the production of the longest leaf blade showedthat, under some conditions, this relation can be disturbed.     

The effect of photoperiod and temperature on growth and frost resistance of winter rye root systems

Root growth, development and frost resistance were examined in winter rye ( Secale cereale L. cv. Puma) plants grown under 6 combinations of temperature and photoperiod (20/16°C or 5/3°C, day/night; 8, 16- or 24-h days). Overall root system growth is influenced by the interaction of temperature and photoperiod. Maximum shoot growth occurs at a 24-h photoperiod in 20°C plants and at a 16-h photoperiod in 5°C plants, and is correlated in both treatments with a high root:shoot ratio. Frost resistance of rye roots is affected by short photoperiods in 2 ways. First, short photoperiod and low temperature delay production of new adventitious roots so that newly developing roots are not exposed to freezing temperatures. Second, short photoperiod alone can induce several degrees of frost tolerance in existing roots during the lag phase of growth. Low temperature alone does not decrease the rate of dry weight accumulation in rye root systems, but cold temperature does retard developmental processes within the roots. Rye roots grown at 5°C develop first order lateral roots, differentiate metaxylem vessels and suberize endodermal cell walls more slowly than roots grown at 20°C.