Plant Growth Regulators INCYDE and TD-K Underperform in Cereal Field Trials

Using plant growth regulators to alter cytokinin homeostasis with the aim of enhancing endogenous cytokinin levels has been proposed as a strategy to increase yields in wheat and barley. The plant growth regulators INCYDE and CPPU inhibit the cytokinin degrading enzyme cytokinin oxidase/dehydrogenase (CKX), while TD-K inhibits the process of senescence. We report that the application of these plant growth regulators in wheat and barley field trials failed to enhance yields, or change the components of yields. Analyses of the endogenous cytokinin content showed a high concentration of trans-zeatin (tZ) in both wheat and barley grains at four days after anthesis, and statistically significant, but probably biologically insignificant, increases in cisZ-O-glucoside, along with small decreases in cZ riboside (cZR), dihydro Z (DHZ), and DHZR and DHZOG cytokinins, following INCYDE application to barley at anthesis. We discuss possible reasons for the lack of efficacy of the three plant growth regulators under field conditions and comment on future approaches to manipulating yield in the light of the strong homeostatic mechanisms controlling endogenous cytokinin levels.

Sucrose interferes with endogenous cytokinin homeostasis and expression of organogenesis-related genes during de novo shoot organogenesis in kohlrabi

Cross-talk between phytohormones and sugars is intensely involved in plant metabolism, growth and regeneration. We documented alterations in cytokinin (CK) homeostasis in four developmental stages during de novo shoot organogenesis (DNSO) of kohlrabi (Brassica oleracea var. gongylodes cv. Vienna Purple) seedlings induced by exogenous CKs, trans-zeatin (transZ) and thidiazuron (TDZ), added together with elevated sucrose concentration (6% and 9%). Significant impact of CK and sucrose treatment and their interaction was recorded in all investigated stages, including plantlet development before calli formation (T1 and T2), calli formation (T3) and shoot regeneration (T4). Results showed remarkable increase in total CK levels for transZ treatment, particularly with 9% sucrose. This trend was observed for all physiological and structural groups of CKs. Application of TDZ contributed to little or no increase in CK levels regardless of sucrose concentration. Analysis of expression profiles of organogenesis-related genes involved in auxin transport, CK response, shoot apical meristem formation and cell division revealed that higher sugar concentration significantly downregulated the analysed genes, particularly in T3. This continued on TDZ, but transZ induced an opposite effect with 9% sucrose in T4, increasing gene activity. Our results demonstrated that phytohormone metabolism might be triggered by sucrose signalling in kohlrabi DNSO.

Limitation of Cytokinin Export to the Shoots by Nucleoside Transporter ENT3 and Its Linkage with Root Elongation in Arabidopsis

The trans-membrane carrier AtENT3 is known to transport externally supplied cytokinin ribosides and thus promote uptake by cells. However, its role in distributing either exogenous or endogenous cytokinins within the intact plant has not hitherto been reported. To test this, we used ent3-1 mutant Arabidopsis seedlings in which the gene is not expressed due to a T-DNA insertion, and examined the effect on the concentration and distribution of either endogenous cytokinins or exogenous trans-zeatin riboside applied to the roots. In the mutant, accumulation of endogenous cytokinins in the roots was reduced and capacity to deliver externally supplied trans-zeatin riboside to the shoots was increased suggesting involvement of equilibrative nucleoside (ENT) transporter in the control of cytokinin distribution in the plants. Roots of ent3-1 were longer in the mutant in association with their lower cytokinin concentration. We concluded that the ENT3 transporter participates in partitioning endogenous cytokinins between the apoplast and the symplast by facilitating their uptake by root cells thereby limiting cytokinin export to the shoots through the xylem. Dilution of the mineral nutrient solution lowered endogenous cytokinin concentration in the roots of both wild type (WT) and ent3-1 plants accompanied by promotion of root elongation. Nevertheless, cytokinin content was lower, while roots were longer in the ent3-1 mutant than in the WT under either normal or deficient mineral nutrition suggesting a significant role of ENT3 transporter in the control of cytokinin level in the roots and the rate of their elongation.

Improvement of Tillering and Grain Yield by Application of Cytokinin Derivatives in Wheat and Barley

Three cytokinin derivatives (CKd) designated as RR-G, RR-O, and RR-V applied by foliar spraying at tillering, and one compound previously described as a cytokinin antagonist (CKa) designated as RR-P applied as a seed coating were tested in winter wheat and spring barley in field trial experiments. The aim of the study was to examine the influence of the compounds that were tested on the number of productive tillers, grain yield, and endogenous CK content. With the exception of the compound RR-V, the measured parameters clearly showed the stimulatory effects of CKd on tillering and grain yield in spring barley and winter wheat. The RR-V showed a stimulatory effect on the number of productive tillers and yield in spring barley, but not in winter wheat. Although in winter wheat CKa stimulated both the number of productive tillers and the grain yield, there was an inhibitory effect in terms of the number of productive tillers observed in spring barley. The results of the endogenous cytokinin analysis suggested, among others, the importance of the role of isopentenyl-adenine types of cytokinins in the tillering of spring barley. In conclusion, the cytokinin derivative compounds with an agonistic or antagonistic role showed strong potential for application in the future development of plant growth regulators.

Cytokinin Signaling Is Essential for Organ Formation in Marchantia polymorpha

Cytokinins are known to regulate various physiological events in plants. Cytokinin signaling is mediated by the phosphorelay system, one of the most ancient mechanisms controlling hormonal pathways in plants. The liverwort Marchantia polymorpha possesses all components necessary for cytokinin signaling; however, whether they respond to cytokinins and how the signaling is fine-tuned remain largely unknown. Here, we report cytokinin function in Marchantia development and organ formation. Our measurement of cytokinin species revealed that cis-zeatin is the most abundant cytokinin in Marchantia. We reduced the endogenous cytokinin level by overexpressing the gene for cytokinin oxidase, MpCKX, which inactivates cytokinins, and generated overexpression and knockout lines for type-A (MpRRA) and type-B (MpRRB) response regulators to manipulate the signaling. The overexpression lines of MpCKX and MpRRA, and the knockout lines of MpRRB, shared phenotypes such as inhibition of gemma cup formation, enhanced rhizoid formation and hyponastic thallus growth. Conversely, the knockout lines of MpRRA produced more gemma cups and exhibited epinastic thallus growth. MpRRA expression was elevated by cytokinin treatment and reduced by knocking out MpRRB, suggesting that MpRRA is upregulated by the MpRRB-mediated cytokinin signaling, which is antagonized by MpRRA. Our findings indicate that when plants moved onto land they already deployed the negative feedback loop of cytokinin signaling, which has an indispensable role in organogenesis.

Kadar pati akar dan sitokinin endogen pada tanaman teh menghasilkan sebagai dasar penentuan pemangkasan dan aplikasi zat pengatur tumbuh

ABSTRAK Pemangkasan pada tanaman teh dilakukan salah satunya untuk menginisiasi tumbuhnya banyak tunas sebagai bakal pembentukan pucuk peko. Pemangkasan mengubah luas daun, kapasitas fotosintesis perdu, mempengaruhi keseimbangan metabolisme antara organ di atas dan di bawah tanah dengan mengurangi jumlah tumbuh tunas yang berfungsi sebagai sumber dan pengguna untuk nutrisi dan hormon. Sampai saat ini pertumbuhan tunas sebagai bakal daun setelah pemangkasan terjadi secara alami tanpa penambahan zat pengatur tumbuh (ZPT). Pada dasarnya rekayasa fisiologis dengan menggunakan ZPT sitokinin dapat menjadi pilihan untuk lebih memacu pertumbuhan cabang lateral dan tunas serta memecahkan dormansi pucuk. Tujuan penelitian pendahuluan ini adalah untuk mengetahui kadar pati akar, kadar sitokinin endogen, serta status hara tanah guna menentukan waktu pemangkasan yang tepat dan dasar untuk dilakukan aplikasi zat pengatur tumbuh setelah dipangkas. Penelitian selanjutnya adalah penggunaan sitokinin BAP pada berbgai dosis pada tanaman teh yang sudah dipangkas. Penelitian pendahuluan dilakukan pada bulan Agustus hingga Oktober 2017 di kebun percobaan Pusat Penelitian Teh dan Kina (PPTK) Gambung pada ketinggian 1250 m di atas permukaan laut (dpl). Metode pengambilan sampel daun, akar, dan tanah di lapangan dilakukan secara komposit untuk setiap ulangan selanjutnya dilakukan analisis pati akar, sitokinin endogen serta hara tanah. Hasil uji kualitatif pati akar menggunakan iodium mengindikasikan bahwa tanaman teh siap untuk dipangkas terlihat dari sampel akar yang ditetesi iodium menunjukkan warna hitam. Hasil analisis laboratorium menunjukkan bahwa kadar pai akar berada pada kisaran 6.99 % hingga 9,16% dan sitokinin endogen ada pad akisaran 0,0016% hingga0,0019%. Penentuan kadar pati akar, kondisi lingkungan serta status hara sebelum pemangkas diperlukan agar meminimalisasi tingkat kematian perdu teh serta analisis sitokinin endogen diperlukan untuk lebih mengoptimalkan dosis sitokinin yang akan diberikanKata Kunci : pemangkasan, sitokinin endogen, kadar pati akar. ABSTRACT Pruning on tea plants is perfomed initiating growth of shoots to be pecco stadia. Pruning changes the leaf area, the capacity of photosynthetic tea bush, affecting the metabolic balance between upper and underground organs by reducing the growing number of buds that function as sources and sinks for nutrients and hormones. Until now the growth of shoots as leaf will after pruning occurs naturally without the addition of plant growth regulating substances (PGR). Essentially physiological engineering using cytokinins can be an option to increase the growth of lateral branches and buds as well as break the shoot dormancy. The preliminary study was conducted from August to October 2017 at experimental field of Gambung Tea and Quinine Research Center (PPTK) at an altitude of 1250 m above sea level (asl). Preliminary method used in the form of analysis of root starch, endogenous cytokinin and soil nutrients to determined the proper pruning time and the basis for the application of plant growth regulator substances after pruning. The results of a qualitative test of root content using iodine indicated that the tea plant was ready to be pruned visible from the root samples that iodized spots showed black. The result of laboratory test showed that root starch content was in the range of 6.99 to 9.16. and cytokinin endogen preliminary analysis showed that the levels are in the range of 0.0016 up to 0.0019. Determination of root starch, environmental conditions and nutrient status before pruning is necessary in order to minimize mortality rate of tea bush as well as analysis of endogenous cytokinin is needed to further optimize the dose of cytokinin to be given. Keywords : cytokinins, pruning, root starch content

The possible relation between cytokinins and secondary xylem formation in Pinus silvestris. I. Seasonal correlations

The Seasonal dynamics of changes in the endogenous cytokinin level was investigated in the tissue of the stem cambial region, The results of the soybean test and Amaranthus test show that marked variations occur. in the course of the year in cytokinin activity in five fractions obtained from tissue of the cambial region. These variations characterized by a spring maximum and late-summer maximum may be correlated in time with changes in cambial activity and the course of annual ring differentiation in the pine stem during the vegetation season.