Viability of Stylosanthes guianensis under different salinity stresses
Plant viability illustrates the level of tolerance of
S. guianensis to salinity stress, which is very important specially to evaluate the quality and growth potential of
S. guianensis. The results of
S. guianensis viability with different NaCl levels (30 DAT) are presented in Fig 1. Viability of
S. guianensis cv. Cook decreased as the NaCl level increased. Media treated with NaCl at the highest level had lower growth by 40% than without NaCl. The decrease in viability occurs due to increased osmotic stress, impaired nutrient absorption, cell death and even excessive Na+ and Cl- ion poisoning, thus disrupting cell ionic balance and physiological processes such as respiration and photosynthesis. In accordance with the research of
Veraplakorn et al., (2013) excess Na
+ and Cl
- ions damage the cell membrane of
S. guianensis so that the metabolic process is disrupted, severe cell membrane damage causes plant cell death.
Growth stages can show different sensitivity to salinity stress.
(Tolib et al., 2017) reported that legumes are still tolerant in moderate salinity soils at 2500 ppm and are not resistant to high salinity. NaCl stress causes plant cell death and reduced growth (up to 40%) either by inhibiting water uptake or toxic effects of ions in the cell. According to
(Farooq et al., 2017) ion toxicity in plant tissues damages cell structure and enzyme function thereby inhibiting growth and causing plant development to be inhibited up to 70%.
Vertical height of S. guianensis under different salinity stresses
The results of vertical height of
S. guianensis at different NaCl levels are presented in Table 1. Giving the highest level of NaCl had a very significant effect at 15 DAP. Media without NaCl (control) showed the best vertical height compared to
S. guianensis with NaCl media. The decrease in vertical height of
S. guianensis was influenced by the level of NaCl which caused differences in the expression of plant height in each treatment. This results in cell damage in
S. guianensis inhibiting growth.
The concentration of NaCl in the media affects osmosis and causes water to move out of
S. guianensis cells. Based on
Veraplakorn et al., (2012) the height growth of
S. guianensis CIAT184 began to be significantly inhibited at a salinity of 20-25 mM NaCl (about 1100-1400 ppm). According to
Chen et al., (2023), an increase in osmotic pressure causes cell turgor pressure to decrease so that stem growth is inhibited and as a result, plants become short. Excess Na
+ and Cl
- ions in the media interfere with the activity of gibberellin hormone in
S. guianensis. Gibberellin hormone plays a role in cell elongation, excess Na
+ and Cl
- ions in gibberellin activity causes inhibited stem growth (
Ramadhani and Ulpah, 2022).
Number of trifoliate leaves under different salinity stresses
Stylosanthes guianensis has trifoliate leaves or consists of three leaflets attached to one stalk. The results of the number of trifoliate leaves at different NaCl levels are presented in Fig 2. Trifoliate leaves began to form on day 12 with the highest number in media without NaCl. The provision of more NaCl caused a decrease in the number of trifoliate leaves reaching 72.7% of the media without NaCl (control). The ability of NaCl can reduce the absorption of water by the roots, the potential water in the media becomes lower than the potential water in the root cells.
Media supplemented with NaCl can increase osmotic pressure, so that plants are dehydrated and interfere with the division of meristematic cells responsible for the formation of primordial leaves of
S. guianensis. According to
Rizki et al., (2022) the number of
Stylosanthes trifoliate leaves at two weeks after planting in the range of 3-6 leaves.
Zhao et al., (2021) reported that salinity stress affects the slow formation of primordial leaves, so it is necessary to have genetic mutations that can protect plants from this stress. Salinity stress inhibits respiratory enzymes and increases free radicals, thus impairing leaf respiration of
S. guianensis. In line with the statement of
Das et al., (2019) salinity stress inhibits the activity of enzymes such as
pyruvate dehydrogenase and
isocitrate dehydrogenase that play a role in cellular respiration.
Number of leaves of s. guianensis under different salinity stresses
The results of the number of leaves of
S. guianensis against different NaCl levels have been done presented in Table 2. The higher the NaCl level in the media, the fewer leaf blades produced. The decrease in the number of leaves shows a significant inhibitory effect on the number of leaves due to high NaCl levels. The impact will be increasingly visible as the level and duration of NaCl exposure increase in the media. High NaCl levels in the media interfere with nutrient absorption by means of Na
+ ion concentrations competing with K
+, Ca
2+ and Mg
2+ ions in
S. guianensis cells and can interfere with cell metabolism. In line with the research of
Feng et al., (2020) which states that Na+ ions have a high affinity which causes the absorption of nutrient ions to be inhibited, so that photosynthesis is disrupted and leaf growth is inhibited. High NaCl concentrations increase reactive oxygen species in plant cells, inhibit axillary branching and reduce leaf blade production
Chauhan et al., (2024).
Leaf length of s. guianensis under different salinity stresses
The difference in leaf surface area significantly affects the rate of photosynthesis that takes place in
S. guianensis. The results of leaf length of
S. guianensis with different NaCl levels are presented in Table 3. Long-term exposure to NaCl and high NaCl levels can cause the growth of
S. guianensis leaf length to be inhibited. The provision of higher levels of NaCl causes water stress, as a result the water content transported for photosynthesis is reduced.
High NaCl levels can be toxic to
S. guianensis by damaging cells and inhibiting metabolic processes. This process disrupts the process of cell division at the leaf growth point, so that the leaves cannot grow optimally long. Research by
Feng et al., (2020) showed that higher NaCl causes water stress, thus reducing the availability of water for photosynthesis and inhibiting the activity of photosynthetic enzymes, such as RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) which is important in CO
2 fixation. Disruption of photosynthesis causes leaf damage and leaf length growth is not optimal. In accordance with
Zhao et al., (2021) If the plant lacks water, the photosynthetic rate will drop, so that cells will be regulated to perform limited growth.
Fresh weight of S. guianensis under different salinity stresses
The measurement results of
S. guianensis weight with different NaCl levels are presented in Fig 3. The highest NaCl level (P4) showed the most significant decrease in
S. guianensis weight (25.97%) compared to media without NaCl (control). NaCl application to
S. guianensis causes dehydration due to NaCl ions pulling water out of the cells, reducing turgor and inhibiting growth. In accordance with
Liu et al., (2017) high salinity causes damage to cell structures resulting in loss of cell turgor and cell death which results in the growth of
S. guianensis being inhibited. Prolonged exposure to NaCl and high levels in tissue culture media can result in necrosis (cell death) of apical buds and young leaf tissue. Tissue death in
S. guianensis directly reduces mass, so the weight of
S. guianensis is reduced.
Hossain et al., (2024) stated that the provision of higher NaCl levels in legumes [
Vigna mungo Hepper] resulted in a decrease in fresh and dry weights due to a decrease in photosynthetic capacity and osmotic imbalance in plant tissues.
Stress index of S. guianensis cv. cook
Salinity stress index is an important method to measure crop tolerance to salinity stress. This method can be used to develop plant varieties that are more tolerant to salinity. The results of the calculation of the stress index in
S. guianensis cv. Cook at different NaCl levels are presented in Table 4. Moderate stress began to appear at 3000 ppm salinity, which indicates
S. guianensis cv. Cook is not tolerant to moderate salinity. The increase in index value is due to the high NaCl level damaging the cell membrane, thus disrupting the metabolism and physiology of
S. guianensis cv. Cook.
Exposure to NaCl in the media also triggered changes in gene expression in
S. guianensis cv. Cook and has an impact on the stress index value. This indicates that
S. guianensis cv. Cook does not have the ability to adapt to medium-high salinity because it experiences a significant reduction in growth. According to
Fuentes et al., (2010)
S. guianensis cv. CIAT-184 shows moderate tolerance to salinity conditions, growth begins to be suboptimal in moderate to high salinity soils. Salinity stress in
S. guianensis cv. Cook increased
peroxidase and decreased root nodulation. Salinity stress inhibits root nodulation by suppressing the growth of rhizobium bacteria that are sensitive to saline areas
(Yunus et al., 2024). Based on
Ghosh et al., (2025) reported that plants exposed to salinity stree need calsium and potassium supplementation to increase protein fraction.
Leaf color of S. guianensis under different salinity stresses
Leaf color is an important parameter to provide information on stress, health and nutrient content in plants. The observation results of
S. guianensis leaf color at different NaCl levels are presented in Table 5. The number after GY/Y indicates the brightness of the leaf, where a higher number indicates a lighter color. The value after the slash represents chroma, with high numbers indicating a more saturated and intense color, while low numbers indicate a more muted color. The leaf color of
S. guianensis (Table 5) in NaCl supplemented media showed green-yellow and dark yellow colors, while without NaCl was dominated by 5GY 3/4 at 36%, meaning that the leaf color has two shades, namely GY (Green-Yellow) with 3/4 which tends to be higher. The more chlorophyll in the leaves, the more green the color response is expressed
(Prihantoro et al., 2023). Exposure to NaCl in the media affects leaf color due to excess NaCl uptake, which inhibits water absorption and stimulates abscisic acid and anthocyanin production, causing leaf wilting.