The purpose of this study was to analyze the effect of Zn nutritional status on the content of pigments, nonstructural carbohydrates, foliage proteins and amino acids of the pecan tree, as possible bioindicators of Zn deficiency. The experimental design was completely random with three Zn nutritional statuses: Normal, Intermediate and Deficient, being selected considering visual symptomatology. On all three nutritional statuses, the concentration of photosynthetic pigments was determined as well as of total soluble proteins and amino acids. Obtained results indicate that Zn deficient nutritional status was characterized by minimum photosynthetic pigment, protein concentrations, maximum amino acid and nonstructural carbohydrate concentrations. While the normal Zn nutritional status presented maximum photosynthetic pigments, proteins concentrations, minimum amino acids and carbohydrate concentrations. On the other hand, intermediate Zn nutritional status was characterized by a medium level between the other two Zn nutritional statuses. Finally, we stress the fact that pigments, proteins, amino acids and nonstructural carbohydrates may be good physiological indicators related to Zn nutritional status on pecan trees.
Mexico is the world’s second largest producer of pecan tree [Carya illinoinensis (Wangenh.) K. Koch], right behind the United States [
In Mexico, the predominating type of soil in pecan tree producing regions is calcareous soil [
Under such soil conditions, as pH increases, extractable Zn decreases due to the increase in adsorption capacity, formation of hydrolyzed Zn forms, and possible chemisorption of calcium carbonate and coprecipitation of iron oxide [
A level below 60 ppm in pecan tree leaves cultivated in alkaline soils of the northern region of Mexico is considered as deficient [
On the other hand [
The study was carried out in the “Tierra Blanca” orchard in Matamoros, Coahuila de Zaragoza, Mexico. The county has 25˚25' latitude, 103˚18' longitude and is at 1150 meters above the sea level. Weather in the county has very dry, very warm and warm subtypes. Average yearly temperature is 22˚C to 24˚C and average yearly rainfall is within the range of 200 to 300 millimeters, with a rainfall regime in the months from May to October. Prevailing winds blow from the south at a speed from 27 to 44 km h−1. Frost frequency is of 0 to 20 days and hail from 0 to 1 day.
The experiment was executed during the month of May 2017 in trees of 6 years of age from the Burkett variety. This variety is characterized by 42 walnuts per pound and a nut percentage of 59%. These trees were located in the nursery within the orchard, with the purpose of rejuvenating the oldest trees. The trees were located at a distance of 1 × 50 cm. Furrows were covered with plastic protective sheets. Irrigation was distributed by means of dripping once per week for a period of 12 hours, from the month of March to mid-October. The area was managed with minimum tilling.
A fully random experimental designed was used, with three Zn nutrition status: Normal, Intermediate and Deficient (
The plant material was selected in accordance with leaflet appearance in terms of color, shape and branch size due to Zn nutrition status. Three nutrition statuses were selected: (a) Normal, (b) Intermediate and (c) Deficient (
Per each nutritional status and its respective repetitions, 40 leaflets of the
growth year leafs were taken in the mid part of the treetop from all four compass points. Plant material was placed on transparent plastic bags and was frozen at −30˚C to then determine photosynthetic pigments, nonstructural carbohydrates, proteins and total soluble amino acids concentrations.
The total chlorophyll concentration was quantified by extraction with methanol and reading the absorbance. For this, 60 mg of petiolules of 5 mm in diameter were weighed, placed in test tubes with 5 ml of methanol, and left 24 h or more until total discoloration of the plant material. The process was made at ambient temperature in darkness. Afterwards, the absorbance was read in 652 nm, the total chlorophyll content was expressed in mg g−1 fresh weight (FW) [
C h l a = [ 15.65 ( A 666 ) − 7.34 ( A 653 ) ]
C h l b = [ 27.05 ( A 653 ) − 11.21 ( A 666 ) ]
C a r o t e n o s = [ ( 1000 A 470 ) − 2.86 ( C h l a ) − 129.2 ( C h l b ) ] / 221
Carbohydrates were measured with appropriate adaptations being made for our plant material. A sample of 0.5 g fresh matter was homogenized twice with 95% ethanol (v/v) and washed with 70% ethanol (v/v), followed by centrifugation at 1500 g at 2˚C for 15 min. Glucose, fructose, and sucrose were determined in the resulting supernatant by spectrophotometry at 650 nm, using the colorimetric assay with anthrone. The total non-structural carbohydrates content was expressed in mg g−1 FW [
The amino acids and proteins were determined after homogenization of 0.5 g fresh samples in 50 mM cold KH2PO4 buffer at pH 7 and centrifugation at 12,000 g at 4˚C for 15 min. The resulting supernatant was used for the determination of total amino acids by the ninhydrin method; total free amino acids were expressed as mg g−1 FW. Soluble protein was measured with Bradford G-250 reagent and expressed as mg g−1 FW, using bovine serum albumin (BSA) as standard [
Data were subjected to a simple ANOVA at 95% confidence, using [
Photosynthetic pigments in pecan trees are indicators of Zinc nutrition status [
The aforementioned can be related to lower Zn concentrations recorded in leaf analysis, with an average of 14.29 ppm. [
Previous studies from [
Zn nutritional status | Chla/Chlb | Chla/Carotenoids | Chlb/Carotenoids | Chltot/Carotenoids |
---|---|---|---|---|
Normal | 1.9181 | 5.0401 | 2.6285 | 7.6679 |
Intermediate | 2.3398 | 4.9710 | 2.0872 | 7.0954 |
Deficient | 1.7171 | 5.2561 | 3.1299 | 8.3171 |
Chla = Chlorophyll a, Chlb = Chlorophyll b, Chltot = Chlorophyll total. The ratio was calculated by dividing the concentration of leaf pigments (mg g−1 FW).
obtained results were larger photosynthetic pigments on the normal nutrition status are shown, match with results obtained by [
There is little information in regards to the effect of Zn nutrition status on photosynthetic pigment concentration of pecan trees. On our study, Chla/Carotene, Chlb/Carotene and Chltot/Carotene relationships revealed that carotene concentrations were higher to those of pigments in a deficient nutrition status compared to a healthy nutrition status (
Zn is closely related to N metabolism, therefore is also tightly related to NO3 assimilation final products on plants, which basically are amino acids and proteins. Proteins are synthesized from reduced amino acids [
important role in nitrogenous metabolism regulation and therefore in protein and amino acid concentration. When Zn is suppressed, protein concentration decreases and amino acid concentration increases. Once Zn is provided again, protein synthesis is induced which results in a decrease in ribonucleic acid (RNA). This is attributed to lesser activity of Zn polymerase, to lower ribosome structural integrity and to higher RNA degradation. The tendency of the deficient nutrition status compared to the normal status in terms of having a lower protein accumulation and higher amino acid accumulation matches with what is mentioned by [
Carbohydrates are the final product of substances synthesized during photosyn-
thesis, during which chlorophyll intervenes actively [
Since the results obtained on this study match with what was reported by [
Zn deficient nutrition status was characterized by minimum photosynthetic pigments and proteins concentrations and by maximum amino acid and nonstructural carbohydrate concentrations. While normal Zn nutrition status presented maximum photosynthetic and protein concentration status and minimum concentrations for amino acids and carbohydrates. On the other hand, intermediate Zn nutrition status was characterized by presenting a medium level compared to the other two Zn nutrition statuses. This behavior can be attributed to the registered low level of Zn. Finally, it is important to mention that pigments, proteins, amino acids and nonstructural carbohydrates may be good physiological indicators related to Zn nutrition status.
Acevedo-Barrera, A.A., Sánchez, E., Yáñez-Muñoz, R.M., Soto-Parra, J.M., Lagarda-Murrieta, Á., de Paul Álvarez-Reyna, V., Madero-Tamargo, E. and Moreno-Resendez, A. (2017) Role of the Zinc Nutritional Status on Main Physiological Bioindicators of the Pecan Tree. Agricultural Sciences, 8, 1327-1336. https://doi.org/10.4236/as.2017.812096