Press Sap Research Articles

USE OF BEST MANAGEMENT PRACTICES TO INCREASE NITROGEN USE EFFICIENCY AND PROTECT ENVIRONMENTAL QUALITY IN A BROCCOLI-CORN ROTATION OF CENTRAL MEXICO

Underground water reserves in Central Mexico have been declining and NO3 − -N concentrations of some irrigation wells have been found to exceed 10 ppm. There is the need to develop best management practices (BMPs) that can increase N and water use efficiency by vegetables such as broccoli (Brassica oleracea L. Italica Group) in this region. Three field experiments were conducted during 1996 through 1998 at the Experimental Station of INIFAP in Celaya, Gto., Mexico to develop BMPs for the region. To determine the N sufficiency levels in the most recently fully expanded leaf (MRFEL), dry midrib and press sap were analyzed for total N and NO3 − -N. Maximum marketable yields of 24.5 to 27.0 ton ha−1 were attained with rates of 400 to 425 kg N ha−1. Sufficiency levels for N in the MRFEL were in the range of 5.5 to 6.5% at the beginning of the season, and then it was reduced to 5.5 to 6.0% at heading and then to 4.0–5.0% during the preharvest stage. The critical NO3 − -N concentration in the midrib ranged from 15,000 to 20,000 mg kg−1 at the beginning of the season to 3,500–5,000 mg kg−1 for the pre-harvest stage of development. The adequate levels of NO3 − -N in press sap ranged from 1,600–2,000 mg L−1 at the beginning of the season to 500–800 mg L−1 during pre-harvest growth stage. Broccoli fertilized with 400 kg N ha−1 provided residual effects in the following crop of maize (Zea mays L.), equivalent to 60% of that produced with N fertilizer. This study shows that drip irrigation, spoon feeding of N, monitoring of N status during the growing season and crop rotations with grains has the potential to increase the N fertilizer use efficiency for vegetables grain cropping systems and contribute to protecting environmental quality in Central Mexico.

Rapid effects of nitrogen form on leaf morphogenesis in tobacco.

Ammonium (NH4+) instead of nitrate (NO3-) as the nitrogen (N) source for tobacco (Nicotiana tabacum L.) cultivated in a pH-buffered nutrient solution resulted in decreased shoot and root biomass. Reduction of shoot fresh weight was mainly related to inhibition of leaf growth, which was already detectable after short-term NH4+ treatments of 24 h, and even at a moderate concentration level of 2 mM. Microscopic analysis of the epidermis of fully expanded leaves revealed a decrease in cell number (50%) and in cell size (30%) indicating that both cell division and cell elongation were affected by NH4+ application. Changes in various physiological parameters known to be associated with NH4(+)-induced growth depression were examined both in long-term and short-term experiments: the concentrations of total N, soluble sugars and starch as well as the osmotic potential, the apparent hydraulic conductivity and the rate of water uptake were not reduced by NH4+ treatments (duration 1-12 d), suggesting that leaf growth was neither limited by the availability of N and carbohydrates, nor by a lack of osmotica or water supply. Although the concentration of K+ in leaf press sap declined in expanding leaves by approximately 15% in response to NH4+ nutrition, limitation of mineral nutrients seems to be unlikely in view of the fast response of leaf growth at 24 h after the start of the NH4+ treatment. No inhibitory effects were observed when NH4+ and NO3- were applied simultaneously (each 1 mM) resulting in a NO3-/NH4+ net uptake ratio of 6:4. These findings suggest that the rapid inhibition of leaf growth was not primarily related to NH4+ toxicity, but to the lack of NO3(-)-supply. Growth inhibition of plants fed solely with NH4+ was associated with a 60% reduction of the zeatine + zeatine riboside (Z + ZR) cytokinin fraction in the xylem sap after 24 h. Furthermore Z + ZR levels declined to almost zero within the next 4 d after start of the NH4+ treatment. In contrast, the concentrations of the putative Z + ZR precursors isopentenyl-adenine and isopentenyl-adenosine (i-Ade + i-Ado) were not affected by NH4+ application. Since cytokinins are involved in the regulation of both cell division and cell elongation, it seems likely that the presence of NO3- is required to maintain biosynthesis and/or root to shoot transfer of cytokinins at a level that is sufficient to mediate normal leaf morphogenesis.

Osmotic Potentials of Water-Saturated Mosses

From 14 species of mosses of the temperate climate osmotic potentials (Ψπ) at full turgidity were determined cryoscopically by use of both extracts produced from dried materials in consideration of the saturation water content and press sap squeezed out from water-saturated plants. With this techniques Ψπ values between −0.5 and −1.0 MPa were found for most of the mesic species. Osmotic potentials measured via freezing point depressions of press sap were about 10–20% higher ( = less negative) than those obtained with extracts from dry mass. In contrast, Ψπ values achieved by use of the conventional plasmolytic method were usually 2 to 3 times lower. It is maintained that these values do not reflect osmolalities at a defined water status and, thus, the plasmolytic method is not qualified for determination of osmotic potentials of leafy bryophytes. Comparison of mosses that were harvested in summer and winter revealed that some species exhibited significantly lower osmotic potentials during the cold season. This can be explained in part by higher sugar concentrations of the more frost-hardy tissues. Generally, the sugars constitute roughly 20–30% of the total osmolality of the cell solution.

Water relations of Picea abies. II. Determination of the apoplastic water content and other water relations parameters of needles by means of capillary microcryoscopy and the pressure‐volume

Using the pressure volume analysis (PV analysis) on the shoots of Norway spruce (Picea abies [L.] Karst.) and the here presented capillary microcryoscopy of the needle press sap of the same shoots, it was possible to determine the amount of apoplastic water in the needles (Wan) as well as in the defoliated shoots (Was). Additionally, the bulk osmotic pressure at full water saturation in the symplast of the needles and defoliated shoots (πon and πos) was determined. The dependence of the bulk‐averaged turgor pressure (Pt) on the water content and the relationship between the bulk modulus of elasticity of the needles (ɛn) and the bulk‐averaged needle turgor pressure (Ptn) was shown with help of the PV analysis on the whole shoots and defoliated shoots. The study was conducted at the end of the vegetation period in 1987 and during winter 1988.The proportion of Wan in the total needle water content (Wtn) was 14% in September 1987 and 12.5% in March 1988. The respective percentage of Was in Wts were 27% and 25%. The amount of apoplastic water depended on the ratio of the dry weight of defoliated shoots to the dry weight of the whole shoots. A standard mean value for the amount of Wan in the total water content of the shoots (Wt) was therefore not possible. The bulk osmotic pressure at full water saturation in the needle symplasts was –1.9 MPa in September 1987 and –2.2 MPa in winter 1988. The respective values of the bulk osmotic pressures in the symplast of the defoliated shoots (πos) were –1.5 MPa and –1.7 MPa. Thus πon was 0.1 MPa lower and πos 0.3–0.4 MPa higher than the average osmotic pressure during full water saturation in the symplast of the whole shoots (πo).The relation between bulk‐averaged turgor pressure and water content showed that during water loss Ptn dropped more rapidly than the turgor pressure of defoliated shoots (Pts). Consequently the needles were less elastic than the defoliated shoots. The turgor values of whole shoots followed an intemediate course between Ptn and Pts. The flat course of Pts seems to be the main reason for the often observed “plateau” of ψ‐isotherms of whole shoots near full turgor.

Influence of potassium nutrition on concentrations of water soluble carbohydrates, potassium, calcium, and magnesium and the osmotic potential in sap extracted from wheat (Triticum aestivum) ears during preanthesis development

For floret development and final grain number ear elongation in wheat (10–17d before anthesis) is the most sensitive period to adverse growth conditions. Sugars are supposedly the main factor determining floret numbers and grain set, and play next to potassium a significant role in establishing turgor pressure in young tissues. In view of this osmotic function, the influence of K on the concentration of water soluble carbohydrates (WSC, total of sucrose and reducing sugars), Ca and Mg was investigated in pot experiments. Further, the osmotic potential of sap extracted from young ears was determined and compared to sap extracted from the leaf blade. Plants supplied with low amounts of K (moderate K-deficiency) had a considerably lower K concentration in the press sap of the flag leaf and the ear than plants well supplied with K. Concentrations of WSC, Ca and Mg were higher in press sap of the flag leaf in K deficient plants than in plants adequately supplied with K. This indicates a substitution of K in its osmotic role. In press sap from ears, however, WSC, Ca and Mg were not influenced by the K application. Therefore, substances other than those measured must have been responsible for the osmoregulation in the young ear. WSC and the osmotic potential increased (more negative) independently on K supply during ear elongation, while K, Ca and Mg concentrations decreased. Whereas grain number was not influenced by the treatment, single grain weight at maturity was reduced by low K availability in the soil.

Sucrose accumulation and osmotic potentials in sugar beet at increasing levels of potassium nutrition

AbstractIn a pot experiment sugar beet Beta vulgaris L. ssp. vulgaris, cv. Kawetina, was grown on alluvial soil (21 mg exchangeable K 100 g−1) containing 0 (K1), 20 (K2), 40 (K3) and 60mg fertiliser K 100 g−1 soil (K4). The plants were sown on 15 March 1983 and harvested on 23 June, 14 July and 30 August 1983. At final harvest root dry weight/plant had reached 269 g in K1 and between 304 and 310 g in K2‐K4. Sucrose values were 15% (K1) and 17.3–17.7% of root fresh weight (K2‐K4) respectively. The osmotic potential of the storage root decreased with increasing K nutrition and time. At final harvest ψ, was between −1.83 (K1) and −2.26 MPa (K4), 75–79% thereof being contributed by sucrose. Sucrose concentrations in press sap increased from 340–400 mM on 23 June to 475 (K1) and 540–570 mM (K2‐K4) at the end of August. In the same period K concentrations declined from 40–100 to 10–35 mM K+. The sucrose, K and Mg concentrations measured in the press sap were lower than those calculated from sucrose, K, Mg and moisture content of the storage root. This indicates that press sap from thawed storage root tissue is not fully representative. Betaine, analysed only at final harvest, significantly increased with increasing K concentrations in the storage root (r=0.83) and a significant linear regression was found between betaine and sucrose accumulation (r=0.57). This is consistent with the role of betaine as a cytosolic osmoticum for sugar beet storage tissue. Other solutes in the cytosol may also contribute to osmoregulation as sucrose accumulates in the vacuoles.

Effect of potassium on the water potential, the pressure potential, the osmotic potential and cell elongation in leaves of Phaseolus vulgaris

The effect of potassium on the water potential, the osmotic potential and the pressure potential in younger and older leaves ofPhaseolus vulgarisgrown in hydroponic culture was studied. Inadequate potassium supply resulted in an increase of the osmotic potential. In the older leaves the water potential was raised, in the younger leaves the pressure potential was depressed in the treatment insufficiently supplied with potassium as compared with leaves with an adequate potassium supply. Cell size of the younger leaves was smaller in the treatment with the low K+supply in comparison with the leaves well supplied with K+. Potassium had a beneficial effect on plant growth, especially on fresh matter production. The water status of leaves (water content, pressure potential, osmotic potential) responded more sensitively to potassium supply than dry matter production. Besides organic N and organic anions, K+was the most abundant solute found in the press sap of the leaves. From the results it is concluded that K+is indispensible for attaining an optimum potential (turgor) in young leaves which in turn has an impact on plant growth.

The influence of ammonia in nutrient solution on growth and metabolism of cucumber plants

Shoot yield of cucumber plants grown 18 days in nutrient solution with 0.06 mM NH3 was decreased. Root yield was diminished at 0.09 mM NH3 The ammonia treatment caused heavy chlorosis increasing with age of leaves. This chlorosis was not due to any nutrient deficiency. Ammonia also influenced the morphology of roots. They were clearly shorter caused by a much smaller size of root cells. The decrease of yield was linked to a reduction of assimilation occurring not only after a long influence of ammonia lasting 14 days, but also within one hour after starting the NH3 treatment. The decline of assimilation was probably caused by a higher resistance of stomata against CO2 influx in leaf tissue as can be concluded from the observation that transpiration was decreased in the same way as assimilation. The effect of ammonia in nutrient solution could also be due to the occurrence of higher NH3 concentrations in leaf tissue, because both, pH of plant press sap as well as NH4 concentration of plant tissue, were increased. Furthermore, it is shown that the nitrate content of plant tissue was diminished by ammonia whereas ammonium and amide content were raised. Regulation of nitrate uptake of plants by means of ammonium and amide content of tissue is discussed.

Effect of silicon on manganese tolerance of bean plants (Phaseolus vulgaris L.)

The effect of silicon on manganese tolerance of bean plants (Phaseolus vulgaris L. var. ‘Red Kidney’) grown in water culture was studied at different levels of manganese supply. Without silicon, growth depression and toxicity symptoms occurred already at 5 × 10−4 mM Mn in the nutrient solution. After addition of Aerosil (0.75 ppm Si), the plants tolerated 5 × 10−3 mM Mn and, at a higher silicon supply of 40 ppm, as much as 10−2 mM Mn in the nutrient solution without any growth depression. This increase in manganese tolerance was not caused by a depressing effect of silicon on uptake or translocation of manganese but rather by an increase in the manganese tolerance of the leaf tissue. In absence of silicon, 100 ppm Mn was already toxic for the leaf tissue, whereas with a supply of 40 ppm Si, this ‘critical level’ in the leaves was increased to more than 1000 ppm Mn. At lower manganese levels in the leaf tissue, a molar ratio Si/Mn of 6 within the tissue was sufficient to prevent manganese toxicity. Above 1000 ppm Mn, however, even a much wider Si/Mn ratio (> 20) could not prevent growth depression by manganese toxicity. With54Mn and autoradiographic studies, it could be demonstrated that, in absence of silicon, even at optimal manganese supply (10−4 mM), the distribution of manganese within the leaf blades was inhomogeneous and characterized by spot-like accumulations. In presence of silicon, however, the manganese distribution was homogeneous in the lower concentration range of manganese and still fairly homogeneous in the high concentration range. This effect of silicon on manganese distribution on the tissue level was also reflected on the cellular level. In the presence of silicon, a higher proportion of the leaf manganese could be found in the press sap,i.e., had been transported into the vacuoles, than in the absence of silicon. The increase in manganese tolerance of bean leaves by silicon therefore seems to be primarily caused by the prevention of local manganese accumulation within the leaf tissue which leads to local disorders of the metabolism and, correspondingly, growth depression.

Estimation of the water of hydration in wintering wheat leaves by proton magnetic resonance.

Water of hydration in whole tissues of wheat leaf sheaths was estimated by Kuntz' proton magnetic resonance method as the fraction of water that was withheld by macromolecular restraint from ice formation. The tissues bound up to 0.5 g water per gram dry weight. At −25 °C, which killed all tissues, the proton signals of unfrozen water were of greater magnitude from tissues and press sap of more hardy (frost resistant) plant material.